Adding an auxiliary muffler

[NICAT]

Hi Friends,
I have a 2002 ML320. For months, I had a loud cabin noise that no one in my city could diagnose. In a previous thread here, you guys suggested checking the engine mounts. After replacing them, the issue was mostly resolved, so thank you for that advice.

However, I still notice a low-frequency exhaust-type noise under load, especially during mild uphill driving between 1500 and 2100 RPM. For many people this might be acceptable, but on the highway it becomes noticeable. If there is a way to reduce it, that would significantly improve comfort.

I am not completely sure whether this is true exhaust noise or structure-borne vibration from the engine. I understand that no mount can absorb 100% of vibration, so some transfer is normal. The noise only appears under higher load. On flat roads at the same RPM range, there is no noticeable issue.

Since custom resonators (j-pipe etc) is not really available where I live, I am considering adding an auxiliary baffled muffler at the rear.

Would this create excessive backpressure? Cats have already been replaced with glasspacks, so the system likely has less backpressure than stock.

Any technical insight would be appreciated.

 

[mk378]

Intakes can also make quite a bit of noise which gets louder at high throttle. Is the intake system stock? Are all intake parts in place?

 

[mk378]

Cats have already been replaced with glasspacks,

That isn't helping. Glasspacks have practically no noise suppression when new, and after some use the glass becomes more packed in place and it's basically a straight pipe.

 

[AdmiralYoda]

You are probably experiencing some resonance or droning at a certain combination of load/RPM. As @mk378 mentioned, glass packs will make this worse not better. Replace them with actual resonators.

It sounds like you want things as quiet as can be. Replace the factory muffler with another factory muffler. Your old muffler could have its internals blown out and causes a resonance at a specific load/RPM.

 

[jetman]

yank out all of the interior and lay down a layer or 2 of sound deadening material.
I did this to my C5 corvette that I use for long distance trips with satisfactory results.

 

[HoosierJeeper]

Are you sure all the exhaust mounts are good? I've had bad ones cause anything from minor drones to sounding like stuff was falling off.

 

[The_Jeff]

I agree with the rubber mount idea, whatever you haven't replaced yet. Also if you have any flex joints (or cup & ball) in your exhaust maybe they're opening up slightly with the engine under load twisting.

 

[NICAT]

Intakes can also make quite a bit of noise which gets louder at high throttle. Is the intake system stock? Are all intake parts in place?

Hi. Would bad intakes cause low frequency loud noise ?

yank out all of the interior and lay down a layer or 2 of sound deadening material.
I did this to my C5 corvette that I use for long distance trips with satisfactory results.

Matted doors. And right quarter panel helped most after adding triple layer of mat.

Are you sure all the exhaust mounts are good? I've had bad ones cause anything from minor drones to sounding like stuff was falling off.

Likely good. i will recheck.

It sounds like you want things as quiet as can be. Replace the factory muffler with another factory muffler. Your old muffler could have its internals blown out and causes a resonance at a specific load/RPM.

New muffler for ML320 is difficult to find. Just one shop had Turkey made one. not sure about quality.
However i would like to know i have better access mufflers of other cars if they do the similar job. at least i can try several different versions with more ease
My muffler had rust related small hole under it. i weld closed it and addedd 2mm steel sheet over it.

 

[Speedbird001]

If I'm reading this thread correctly: the cats are removed and the stock muffler (Worn or damaged) was repaired? All bets are off: there are multiple variables here... If you have the $ and time maybe start from scratch: OEM cat and OEM muffler (Check or replace the hangers and any flex pipes/fittings). Good luck. Whatever you do, If you can get your hands on a db meter before and after I'm sure we would all love to see the results

 

[Selmorides]

Just might be the glass packs.

 

[NICAT]

If I'm reading this thread correctly: the cats are removed and the stock muffler (Worn or damaged) was repaired? All bets are off: there are multiple variables here... If you have the $ and time maybe start from scratch: OEM cat and OEM muffler (Check or replace the hangers and any flex pipes/fittings). Good luck. Whatever you do, If you can get your hands on a db meter before and after I'm sure we would all love to see the results

Thanks Sir.
You guys on this forum have always been helpful

 

[researcher]

Thanks Sir.
You guys on this forum have always been helpful

you probably have a cell phone where you live? you could always download a soundmeter app from the apple or google play store, those can measure db sound readings. I thought smart cell phones were everywhere in the world. if I'm wrong, I apologize.

 

[Revving2Redline]

Possible to use exhaust wrap or high temperature grill paint to "insulate" the heat. The hotter the exhaust the faster it will move. Resonated exhaust tips, thermal mat coating, thicker carpet. Last but not least, turn up the radio

 

[NICAT]

you probably have a cell phone where you live? you could always download a soundmeter app from the apple or google play store, those can measure db sound readings. I thought smart cell phones were everywhere in the world. if I'm wrong, I apologize.

Sure Sir. Since i can post in this forum, take image of my muffler during repair and share here, i definitely have access to daily used modern technologies

But are you sure soundmeter apps will be accurate since phone microphones / and their firmwares are not built / calibrated to accurately measure the level of audio ? In my opinion, readings would differ based on the phone models.
I am planning to buy a dedicated device which is around 200$

Possible to use exhaust wrap or high temperature grill paint to "insulate" the heat. The hotter the exhaust the faster it will move. Resonated exhaust tips, thermal mat coating, thicker carpet. Last but not least, turn up the radio

Thanks for suggestion, i will further focus on researching f wrapping exhaust would reduce such type of noise on forums. That would be greatest workaround if successfull

 

[Arc]

Hi. Would bad intakes cause low frequency loud noise ?



Matted doors. And right quarter panel helped most after adding triple layer of mat.



Likely good. i will recheck.



New muffler for ML320 is difficult to find. Just one shop had Turkey made one. not sure about quality.
However i would like to know i have better access mufflers of other cars if they do the similar job. at least i can try several different versions with more ease
My muffler had rust related small hole under it. i weld closed it and addedd 2mm steel sheet over it.

View attachment 325098

That is one big muffler. If the outside casing is getting holes in it it's a safe bet the inside baffles are also shot and maybe broke loose. Scrap that old thing and just buy a different smaller muffler.

 

[AdmiralYoda]

Yup.... now that you mentioned that the original muffler got "repaired" because of rust and holes I'm 99.8% sure the muffler is going to cause noises.

No aftermarket replacement muffler is available? In the US Rockauto, PartsGeek, even Auto zone has options. Not sure how availability works in other regions but I suspect they are available. What about the Mercedes dealership?

 

[The_Eric]

Hi. Would bad intakes cause low frequency loud noise ?

Yes, a modified intake or one missing it's factory parts could definitely increase noise.

I had an old GM 6.2 V8 diesel that I removed the inlets and flipped the air filter lid upside down and it's intake noise was legitimately as loud or louder than the engine (which was plenty diesel rattly) and louder than the exhaust.

 

[mk378]

There's a reason why luxury cars that aren't even this old are cheap on the used market. For multiple reasons they lose their quiet smooth ride and the best course of action for someone who cares about that is to trade for a new one.

 

[NICAT]

Possible to use exhaust wrap or high temperature grill paint to "insulate" the heat. The hotter the exhaust the faster it will move.

I made some research, many states it reduced drone etc. Since easily applicable i would like to give it a try

No aftermarket replacement muffler is available? In the US Rockauto, PartsGeek, even Auto zone has options. Not sure how availability works in other regions but I suspect they are available. What about the Mercedes dealership?

Repair costs are actually quite low in my country for example, a brake pad replacement is only about $7. Because of this, most ML W163 owners here just drive them until they stop. They think If the car starts and drives, it’s good

I actually have muffler from a junkyard. It looks fine on the outside, but I have no idea what the condition is on the inside. I may install it for testing purpose. No welding. just clamps.
There is also a shop here that has a new, Turkish-made muffler for $150 including installation. I’m thinking about asking them for a "test fit" just to see if it fixes the drone!

I’ve noticed something odd, though. I’ve seen many mufflers at shops with thick, patterned shells that are so hard they actually hurt your knuckles when you tap them. But the W163 mufflers have such a large, flat surface area and a relatively thin shell. Even on the top side (where there is no rust), the exterior shell sounds too acoustic compared to other mufflers when you touch it.

I’m wondering how even a stock W163 muffler avoids radiating noise through that shell. I even tested the new Turkish-made one, and its shell didn't feel very stiff either.

 

[NICAT]

Today i went to shop. They told Hangers are fine.
I decided to make an inspection myself.
Guess What. Mercedes designed exhaust hangers covered with metal frame, for failsafe purpose.
So ? Most of the time overstretched hanger that hits bottom of frame gives an illusion of being OK because it is not torn. And dampening potential is significantly reduced.
The rubber at bottom end is freely moving up and down through metal, so provides no dampening effect and usually not torn due to no stress