2006 G35x Sedan 40k miles -- About 2 months ago I noticed a new sound in the back of the car that sounded like a hole in my muffler. I don't hear it if the car is in park and I just rev it, I only hear it when I'm driving ... it gets louder as I accelerate [or at least more pronounced]. My RPMs seem fine. Muffler guy said all looks ok. I beg to differ. Any ideas? Thanks.

Sure its the exhaust and not maybe a bad wheel bearing humming?

All muffler shops are not equal, while it was on the rack did he have you start and rev the engine?? If not find a new muffler shop and tell them what you're hearing...Gary

I guess I can't be sure it's the exhaust since I don't know what it is ... but wheel bearings?...seems that would be more of a thumping or vibration, yes? This sounds like the muffler/exhaust.

Also the muffler guy ... he didn't listen to it while it was on the rack, but ... I don't hear it in 'park' while revving... only when accelerating while driving.

Thanks for your responses....
Further ideas?

Have you layed on your back and had a look?

The muffler flange has a habit of rotting away. Many cars here have had to repair a leak there. Have a friend block the tailpipes with a rag and listen for a "puffing" sound coming from the exhaust indicating a leak.