I'm taking opinions on where/what this noise is coming from.

https://www.youtube.com/watch?v=fIE_4C-f3bI

2006 Corvette Z06.

Seems to come from right around where the shifter is located or a little in front of that and it can be induced by coasting around 60-70 in fifth or sixth and letting off on the clutch. At times it will just decide to start doing this when coasting downhill at that same speed. Can be made to stop doing it by pressing the gas.

Car is completely stock other than shocks, but the thing is, it has made this noise since I got it, before I did anything to it. And nothing I've repaired on the car so far has changed it.

Letting off on the clutch means the engine is idling and the clutch is depressed, or your foot is of the clutch?

I love it when these things give me completely absurd thoughts that are so Rube Goldberg as to be incredibly unlikely, but for your amusement: HVAC. You're not usually doing 60-70mph with idle levels of vacuum... The HVAC doors do something in combination with freeway speed air at the cowl in that combination to make odd noises.

I can even prove myself wrong by the observation that just letting off the gas without putting it in neutral at that speed should provide as much or more vacuum. Unless it's a smart HVAC system that does different things at idle than at speed.

If I were to make some sort of argument for the viability of my long shot, it would be that the HVAC may be run differently at idle, so coasting at 60mph is the only way to induce the combination of settings...

Sorry, I will be cruising at 60-70 downhill, clutch is not depressed, light or no gas and this noise happens sometimes. Not all the time and usually downhill is where it happens most.

I can get it to happen on a more level surface by pushing the clutch in and letting it out fast where I get a bit of a forward jerk from letting off, but again it really seems to be in 5th or 6th at 60-70 where I can make it happen doing that.

It also won't happen at all until the car gets warmed up. It is noticeably absent in colder weather until the car has been going for a while and happens quicker in very warm weather.

Ransom wrote: I love it when these things give me completely absurd thoughts that are so Rube Goldberg as to be incredibly unlikely, but for your amusement: HVAC. You're not usually doing 60-70mph with idle levels of vacuum... The HVAC doors do something in combination with freeway speed air at the cowl in that combination to make odd noises. I can even prove myself wrong by the observation that just letting off the gas *without* putting it in neutral at that speed should provide as much or more vacuum. Unless it's a smart HVAC system that does different things at idle than at speed. If I were to make some sort of argument for the viability of my long shot, it would be that the HVAC may be run differently at idle, so coasting at 60mph is the only way to induce the combination of settings...

Okay, I'm really not ruling anything out, because I've done a bunch of repairs to the car that I thought might cure this noise. I don't want to influence anyone's thoughts on the issue, but I do have a build/project thread for the car.

Even the Corvette forum people haven't heard this one.

It sounds a bit like a bearing cage is trying to climb all over itself. Neons make a similar noise from the trans when they are cold.

I'm at the point where if no one knows what it is I'll just wait for something to break. The only really expensive part of the car is the motor, so I'm just hoping it's not something that could break that.

So it's a noise under "neutral throttle"?

That's usually something related to gear mesh. It's amazing how poorly set up gears can quiet down under load. Could be the transmission telegraphing through the shifter.

The 016 trans in my Quantum would do something similar. Those old Audi transmissions were notorious for R&P noises.

Does it go away if you put light pressure on the clutch pedal?

The sound in the video reminds me of a throw out bearing.

Sounds like a noise my friend had on his C6, his tranny was low on fluid after the dealer did a radiator change. He had paddle shifters but I'm thinking the Z06 has a trans cooler in the radiator?

jstand wrote: Does it go away if you put light pressure on the clutch pedal? The sound in the video reminds me of a throw out bearing.

Yes, it does go away with light clutch pressure it seems.

The Corvetteforum people seem to think throw out bearing as well. If that's actually the case I'd be annoyed since the whole clutch was replaced recently and it says right on the invoice "replace release bearing and slave".

tooms351 wrote: Sounds like a noise my friend had on his C6, his tranny was low on fluid after the dealer did a radiator change. He had paddle shifters but I'm thinking the Z06 has a trans cooler in the radiator?

The C6 Z06 has a trans cooler. Even a manual trans isn't that expensive to replace, but I'd like to know if it's actually the trans.

I wasn't clear, his problem was the transmission was low on fluid and you could hear air in the lines at certain times when driving the car an indy shop filled the trans up and the noise went away. I think checking the fluid is a real pain as far as getting around the exhaust. The dealer said it was torque tube bearings or mounts? I forget which but I remember they were gonna soak the cash right outta him.

tooms351 wrote: I wasn't clear, his problem was the transmission was low on fluid and you could hear air in the lines at certain times when driving the car an indy shop filled the trans up and the noise went away. I think checking the fluid is a real pain as far as getting around the exhaust. The dealer said it was torque tube bearings or mounts? I forget which but I remember they were gonna soak the cash right outta him.

That is an odd problem. Not sure if that applies here as this is a manual versus auto and they replaced the trans fluid when they did the clutch and the noise is the same.

The shop that did the work has a pretty good reputation here in CT so I'm seriously doubtful they intentionally cut corners. Maybe they missed something, but that's as far as I'd go.

So, I sent the noise to the guy that did the whole drivetrain rehab and even he doesn't know what that could be. I'm gonna have to wait for something to break I think before I figure this one out.

It really cannot be the throwout. There is just no way they let that slide and didn't replace it as the old clutch was so burnt up as to be almost unusable. Even if the new throwout was somehow bad, how would it make the exact same noise in the exact same way as the old one?

Harvey wrote: So, I sent the noise to the guy that did the whole drivetrain rehab and even he doesn't know what that could be. I'm gonna have to wait for something to break I think before I figure this one out. It really cannot be the throwout. There is just no way they let that slide and didn't replace it as the old clutch was so burnt up as to be almost unusable. Even if the new throwout was somehow bad, how would it make the exact same noise in the exact same way as the old one?

I'm not thinking the bearing is bad, just that there is certain conditions where it is unloaded enough to make noise. Once you place light pressure on the clutch pedal there is enough pre-load to quiet the bearing down.

Another possibility would be if they didn't reshim the throwout bearing and there is excessive clearance allowing the rattle under certain conditions. If this is the case, it should go away over time as the clutch wears and the clearance is taken up. This condition will usually result in noise in neutral, so it is probably low on the list of causes.

Purely guessing, but a slim possibility is that when unloaded/lightly loaded the shaft splines can float a little in the clutch splines and that movement causes the noise (or causes another part to resonate causing noise).

With the ZF6, the pilot bearing is brass or a brass alloy and the brass is sacrificial in that it is doing the lubricating. Most pilot bearings get a coat of grease when installed but it's a strict no-no in this application. The grease dries out and hardens and the brass can't do it's job. Maybe something similar with your Tremec?

I would guess one of the bearings in the trans is the culprit. I would recommend checking gear oil level and type.
Do these take the thin GM syncromesh fluid?

Problem is the pilot bearing was replaced, the throwout bearing was replaced, the fluid was replaced in both the trans and diff. Noise is the same as before everything was done. So, either they didn't do all that stuff or it's something completely different or maybe it's the trans and it will just break at some point.

I guess I'm just waiting for whatever it is to break or get worse or something.