I have an intermittent rubbing noise that I cannot figure out. I have used the search function and found people with a rubbing noise, however, that seems to be related to turning which this is not. Also people are discussing it from the rear and mine does not seem to be coming from there.

First off this is a 2005 MN6 convertible. I have the Z51 sways on the base suspension. I changed my rear diff fluid a few years back with Amsoil.

The noise sounds like someone is dragging something perhaps like rubber being dragged across a surface. When I first heard this noise I thought I had caught something under my car and so I got out to look, but nothing was there.

The conditions of the noise:

1. Only occurs on first drive of the day if it occurs at all.
2. Occurs in either reverse or 1st gear.
3. No turning of the wheel is required to produce noise.
4. Noise sounds like it is coming from directly under the car perhaps. slightly forward of my seating position. Can also be "felt" in the shifter.
5. First occurred at least a year ago and then never again until recently. Now has occurred roughly 3 times over 2-3 months.
6. Not a large sample size, but when it has happened it has been when the car has sat untouched for at least a day. Again it does not happen every time I leave the car un-driven.
7. Once I am under way the noise immediately goes away and does not come back for perhaps weeks to months.
8. The emergency brake is not on when it occurs.

It is extremely loud when it does happen. You'd swear you were dragging something underneath. Any ideas?

 

My guess:

Oxidation or corrosion/rust on the brake rotors. After just a few brake applications, the brake pads clean off the rust on the rotors and they are shiny and smooth once again.

This can occur after the car sits for a few days, of if you wash it and park it with out driving it.

 

U may have a manual and it could be the clutch or throw out bearing.

 

I really don't think it is from the brakes and I see no rust. This is a different sound than if you wash and don't drive. I think it would happen with more consistency if this were the problem as well.

 

I do have a manual as mentioned. I don't understand what you are saying.

 

The only other thing that comes to mind is that it may be noise from the front U-joint.

 

Is this an issue I should be concerned about? The car is no longer under warranty. Anything I need to do or check? Thanks.

 

Since I really do not know what is causing the noise, I can not say.

 

That would be my guess.

 

Assuming your guess is correct is where my question comes from.

 

Definitely not the problem and it doesn't really rain here. The rotors are clean as they can be and no different than on any other day.

 

I suspect it is diff clutch pack related. After sitting for awhile, the diff fluid will slowly drain out of the diff clutch packs and when you start to drive these clutch packs will "chatter" vice smoothly rotate against one another. This problem seems to be much more common to the C6 than the C5. Though the AMSOIL Severe Gear Extreme Pressure Synthetic 75w90 seems to be much more resistant to this problem than the GM fluid, it is still possible that this is what you are experiencing after long periods of non-use. I suspect you a feeling it farther forward because of the connection between the diff, tranny and torque tube.

The diff "chatter" shouldn't damage anything and if it is going away shortly after you get the fluid back up into the diff clutch plates I don't think I'd worry about it. That said, I have tons of diff fluid lying around my garage, so I might change out the fluid, or add a bottle of the AMSOIL Slip-Lock Differential Additive and see if that helps.

 

The only issue here is that I don't hear a "chatter" type noise at all. My understanding of the rear-diff issue is that the chatter is very noticeable and I think it also happens on turns. Mine is a loud rubbing dragging type noise that occurs in straight lines.