ZenicaPA

My Z06 has a strange hard to describe noise, it occurs between 30mph and 80mph, presumably it does it at higher speeds but I haven't checked. If I apply the accelerator under light engine load, just enough to maintain the current speed on a flat road and then let off the accelerator there will sometimes be a groaning sound under the car.
My wife describes it as a cross between sounding like a twig or branch is being dragged by the car and someone clearing his through in a library.

I'd put money on a wager of what the dealer will say if I bring it to them so I'm hoping someone here can make a suggestion based on this limited description. Perhaps there is a TSB someone is aware of that I can pass along to the dealer. The sound to me sounds like it is coming from a u-joint in the drive shaft but this car doesn't have that, does it?

I tried recording it but ambient sounds are picked up the same by my phone making isolating the sound very difficult. I'm going to see if I can use some software I have to clean it up and isolate the sound.

I'm open to any input that I can pass along to the dealer in an effort to aid them in looking for the source.

Speednet

Probably a transmission problem, I'd suspect, especially if it's an A8. I would definitely get it checked out at the dealer. And maybe do a test drive with the service manager in the car to be sure they are hearing it themselves.

sTz

Do you have an 8A? If so, then possibly a tranny or maybe an eDif problem, but it could also be the more common shutter issue involving the AFM. I suspect the latter.

ZenicaPA

I do have the A8.

I tried having the dealer diagnose another issue with the trans but they brushed my concern aside as unverifiable.

That issue is still present and seems more pronounced as the weather cools, the delayed engagement from P to R or D after sitting overnight. There is a TSB for it but they won't perform it because they haven't duplicated the concern.

This noise doesn't have any discernible vibration or feel to it making it hard to tell where it originates but I get the sense it is middle or rearward of the drivers position.

NSC5

What setting are you using for engine sound management (the NPP exhaust)? In sport or track mode you may have the exhaust flow valves for the "straight through" exhaust pipe shutting off as you transition on and off throttle and one of the valves may be dragging causing the noise. These same valves are used with the Z06 to avoid the horrible exhaust note caused by a V8 operating in V4 mode and one of the few ways to reliably put a Z06 into V4 mode is to coast down or use very light throttle slowing from a higher speed which may be happening under the conditions you described.

Try setting it to stealth mode, go to vehicle settings, engine sound management which leaves the exhaust flow control valves shut under almost all conditions and see if that sound goes away.

Note that these are the NPP valves, the Z06 doesn't have the other valves used in some versions of the C7 to control the exhaust sound in V4 mode as they would get cooked by the exhaust heat from the Z06 running on the track.

ZenicaPA

↑ I was in Touring mode and had the coolant temp showing in the center so I don't recall seeing V4. I have my exhaust locked to Track mode. I'll change the settings as you suggest for a test drive and see.

Thanks for the post.

23/C8Z

not the trans. its a valve in exhaust or possibly the belt tensioner something along those lines. just completed a 200 mi round trip journey today. Z06 went into V4 mode 1x for about 3 seconds. these cars don't go into V4 unless your peddling along at 55. the LT1 (as does my Sierra with 8spd) goes into V4 all the time. annoying.

AORoads

A few days ago I thought I saw you mention that you had not heard of Steve, the Corvette Tech at Bryner. From what I've read about him, he's excellent. I can't diagnose it but maybe he can.

cvwb

Here's the link to the thread with my hard to describe noise:

http://www.corvetteforum.com/forums/...-question.html

Per reply #3, first link, it was the AFM 4/8 cylinder deactivation tensioner belt that caused my noise. Dealer replaced, and all is well now.

http://www.corvetteactioncenter.com/...-afm-1357.html

ZenicaPA

@NSC5

The noise is there, even with the changes you suggested.

I have a service appointment to bring it in. Not being skeptical, just realistic. I KNOW what they will do/say. I may have to try another dealer as AORoads suggested.

smbsocal

Since you have a auto it may be the AFM, the v4 sounds awful and can make the car sound like it has issues. You can always get the Range AFM disabler if you want to disable AFM.

ZenicaPA

I'm reluctant to connect anything or do anything which may afford GM an avenue to block my warranty. Even for the purpose of testing the devices ability to eliminate the issue.
Another thing I can do to see if it is the V4 mode, place the gear select in M as that disables V4 mode.

kenownr

I know exactly what it is; it's the exhaust reflection noise from the Mustangs and P-cars trailing along behind you !! You can spot it easily if you look for the red faces in your mirrors
tom