What do you think this noise is

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Jul 3, 2020
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Hi all, back with another mechanical question. There's this odd noise coming from the engine that I can only hear from the inside with the doors and windows closed. It sounds like a roller or bearing going bad on the serpentine belt, or even worse, the timing belt. However, if I go outside, I can't hear it at all. I used a stethoscope and put it on the metal surrounding the serpentine belt, and also on the timing cover/near the timing belt area to see if I could hear the noise, but I couldn't hear anything strange compared to what I hear inside. I've uploaded a short video, you can definitely hear the noise, it's a deeper noise in the background from the engine noise. I do have the car scheduled for a timing/serpentine belt and water pump job next week, so if it is related to that it should obviously get fixed when everything gets replaced. Just curious if anyone has heard a similar noise before
 
Sounds like a grumbling/rumbling noise? Hard to tell what from the video, but IMO that would be pretty loud for an idler or tensioner pulley on the accessory drive (serpentine). And if it was an idler/tensioner, you could definitely hear it from outside the car so you can pretty much rule that out. Report back after the belt/pump service and let us know if the noise is still happening. Also you might want to state the year/make/model/mileage.
 
Sounds like a grumbling/rumbling noise? Hard to tell what from the video, but IMO that would be pretty loud for an idler or tensioner pulley on the accessory drive (serpentine). And if it was an idler/tensioner, you could definitely hear it from outside the car so you can pretty much rule that out. Report back after the belt/pump service and let us know if the noise is still happening. Also you might want to state the year/make/model/mileage.
Ah completely forgot to write that down. It's a 2013 VW golf tdi with 128000km

I will report back after the belts/tensioners/idlers are replaced for sure
 
I think it is an idler bearing noise. Get a stick and listen to each one.
On the timing belt? Don't really have a way to listen to them individually, the cover is in the way and there's no way to remove it without taking a bunch of other things off (at least from what I can tell)
 
OK. covers off
Can't take the cover off without removing a bunch of ancillary pieces such as fuel lines out of the way. The cover will come off next week at the shop and I'll report back with any findings
 
So timing belt, water pump, and associated rollers/idlers have been replaced, along with the serpentine belt and one tensioner roller which was bad. While the noise has disappated, it's not fully gone, but you have to really be looking for it to even notice it... What it can be at this point, I'm not sure, and to be honest, after comparing with my friends 14 Jetta tdi with the same engine, and hearing other owner reports of similar cars, these tdis seem to resonate all sorts of noises...
 
From inside the car it almost sounds like a rod knock. Can you can a video from outside the car, closer to the engine so we can give you a better idea?
 
From inside the car it almost sounds like a rod knock. Can you can a video from outside the car, closer to the engine so we can give you a better idea?
I don't understand how you even came to that conclusion... You do realize this is a diesel engine right? They all "knock" ... Also, I'm pretty sure rod knock isn't that quiet that it can only be heard from inside the cabin
 
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