haulinkraut

I has noticed an odd groan sometimes when I accelerate after I let off the gas. I notice it whenever my tires loose traction after I let off the gas. Strange. Open differential noises? Any ideas?

Dock

Does it happen when you have not been pulling any boost immediately before letting off the throttle?

haulinkraut

? I do not understand the question. Pulling boost?
Not to be rude BTW. I just don't understand the question.

Macster

Use the on-board computer stalk to cycle through the various items it can display until you come to the boost display.

While driving the car when you step on the gas pedal hard enough you will see that number climb from 0.0bar to 0.1bar, 0.2bar, 0.3bar and so on. Max (unmodified and working properly) 996 Turbo boost should hit 0.7bar somewhere between 2700 and 4500 rpms (give or take).

So, the question: Does it happen when you have not been pulling any boost immediately before letting off the throttle?

is trying to get some more details as to what the exact sequence of events is leading up to and at the time you hear the groaning noise.

Sincerely,

Macster.

haulinkraut

It only seems to happen after I go into full boost and I loose traction. Then it happens for a second and only after I let off the gas from full boost. Could it be a rear wheel bearing that is just getting loaded enough to scream when I hammer it?

Dock

It could be the boost being dumped. Could also be the DVs if they are still stock.

haulinkraut

I have new 710N valves. I have heard boost before, this noise is like a whirring, groaning or humming that sounds mechanical.

raineycd

Maybe traction control or ABS?

haulinkraut

What sounds do those systems make?

Macster

I would have to agree with Dock that the noise is boost being dumped as the tires break loose and the engine rpms flare and excess boost is generated.

Any DV can make the noise. It is just pressure being bled off/from the intake.

But if you don't like that explanation, then if the tires break loose the car can generate all sorts of noises. The rev limiter can kick in and the various drivetrain components as they see load and some unloading as the rev limiter does its thing can make noises that could fit your description.

I've never experienced this with my Turbo (at $1700/set of tires I'm not going to break those suckers loose if I can help it!) but in other cars the rear (and in the Turbo since it is AWD even the front) suspension can hop about, suffer from wheel hop as the tires spin and grab which loads the suspension which rebounds.

At the front of the car, under hard acceleration, the front diff wants to rotate and this puts the cardan shaft under a bit of load/bind. The result is the cardan shaft may flail about (in a very limited sense) but enough to generate a racket.

The forces the car's various components have to absorb/control under hard acceleration is amazing enough but to expect the to car to experience wheelspin and not make some protesting noises of some kind is expecting too much.

Of course, as with any noises out of the ordinary one has to eliminate various other things. If the car has had its suspension modified there's always the question of did something go wrong and did a component come loose or did a component break.

If not one of the modified components then certainly another possibility is one of the stock components may have let go. Repeated hard acceleration takes its toll on the car and its drivetrain, suspension and running gear so at any time something can go bad and the noises you hear may be a warning sign that something has gone bad.

So, you have to carefully and thoroughly check the car out at all 4 corners for any signs of trouble. The noises may be just the result of the way you're driving the car or they may be the result of pending trouble.

Sincerely,

Macster.

haulinkraut

The noise is actually recently shown itself without accelerating. It sounds like a rear wheel bearing to me. I think when I accelerated and the noise happened it was because the bearing was getting loaded just right to make the noise.

Dock

I think that if it is a wheel bearing, you should be able to hear it making noise either while cruising, and/or when loaded up in a turn.

Is there any additional noise coming from the back when cruising or cornering at steady throttle?