The engine sounds louder, now smelling burning oil after an hour of driving.

Hopefully I'm wrong but I thought some of these were known for the cat. converter breaking apart internally. And the broken peices being sucked back into the engine.
I had a 06 1.8 special edition long time ago and I hated the oil filter position since it was directly above the exhaust midpipe. If any leaked on there it would smell like burnt oil for days.
This isn't the SER SpecV is it?
I would have guessed that there aren't many of the 2.5L on the road anymore as the intake manifold had a nasty habit of disintegrating and gradually destroying the engine after the warranty ran out resulting in escalating oil burning and compression loss. There was a recall, but by the time they fixed it the patient was headed to the morgue...
If it was a German car, the burning oil smell would most likely be from leaking valve cover gaskets.
It’s probably a small oil leak somewhere, the vehicle was driven very little for years, so this type of thing is normal once a vehicle is revived to daily duty.

But I would investigate further the engine being louder. Perhaps go for a long drive and hear for yourself.
2006 Sentra, 1.8S (QG18DE engine) with 125K miles on the odometer.

In the past, we would not drive more than 3000 miles a year, but since August 2022, my wife started driving it to work, ~50 miles daily round trip.

For the last couple of months, she is complaining that the engine sounds louder, and now for the last week or so, she mentions a faint burning oil smell in the cabin after an hour of driving (At the end of every trip, never in the beginning). I immediately checked the oil level and it is fine. There is no change in how the car drives. There is no engine light. The oil was changed 3 weeks ago with Mobil 1 5W-30. The filter was hand-tightened. Never experienced oil burning before so can't say much. Her first half-hour drive is on the interstate and the rest half an hour is in bumper-to-bumper crawling city traffic.

I pulled out the PCV valve to check if it was busted. While it's dirty, with significant carbon build-up, it rattles. I tried cleaning unsuccessfully with a brake cleaner. Installed back and the engine sounds the same (louder). I have ordered a replacement PCV Valve. OEM was unavailable locally. I will replace it next weekend.

What else can I check, if anything, or time to call the mechanic?

Thanks in advance.
My bet is on a small valve cover gasket leak, dripping onto the exhaust. It may not be noticeable by the oil level (a whopping 2.9qt oil capacity), but it's there. Just gotta find it.