Rev engine, let off gas, scraping/grinding noise -- wtf?

[swope]

Hey, so I'm finally getting ready to do some performance upgrades on my 2012 A7 3.0t, but I noticed some strange noises last night.

I rev the engine in neutral (with the car stationary) and let off the gas... as the RPMs come down, the car makes a strange scraping/grinding sound at two specific RPM ranges: ~3500 to 3200 and ~1500 to 1200. The noise is louder with the door open and seems to be coming from the driver's side, although I can't pinpoint the location exactly. It happens every time I rev the engine and let off the gas. And ONLY when I'm off the gas.

Any idea of what might be going on here?

[litigator]

Video of it?

[swope]

Sound is most noticeable from 0:05 to 0:06 as engine speed drops from 1500rpm to 1200rpm. It does this at the exact same rev range EVERY time I rev the engine and let of the gas.

[swope]

Another note: it gets louder and more noticeable when the engine is fully warm... It doesn't really make any noise if I rev it over 1500rpm when it's cold/only slightly warm.

[swope]

It seems to be a vibration from below the vehicle on the mid/rear driver's side. When I hold the car at 1400rpms, there is a constant vibration noise from that area. You can hear the sound from 0:05 to 0:07 on this video.

In the video it sound more like a "grind," but it person it sounds more like a "vibration."

Maybe a heat shield rattling against the exhaust?

[///M Traitor]

It's hard to tell from the video, but I'd bet it's something on the exhaust system that is rattling. Like a heat-shield that is loose, or something internal to the Cats. You'll probably need to get the car up on a lift to properly diagnose... The engine vibrations at specific RPMs can cause harmonics that amplify the vibration of attached components.

[swope]

It's hard to tell from the video, but I'd bet it's something on the exhaust system that is rattling. Like a heat-shield that is loose, or something internal to the Cats. You'll probably need to get the car up on a lift to properly diagnose... The engine vibrations at specific RPMs can cause harmonics that amplify the vibration of attached components.

Yeah, that's what I'm thinking too. I plan on having the AWE touring exhaust installed on it next week, along with some other stuff.

Is it worth taking this to the dealership -- 1 hr drive each way and a pain in the ass to find the time to get out there -- to look at it, or just mention it to my mechanic when he installs the new exhaust system?