Mrmojo78

Hello everyone. I have this weird noise that is only audible in gear and accelerating. Sounds like its coming from underneath the car toward the front. Sounds like a sputter or sorry, but a fart in a can. I wish I could describe the sound better. I threw smoke into the exhaust and didnt see any leaks. I looked under the car and in the engine bay and didn't see any signs of burn or carbon build up. I don't know if this is related, I seem to have lost power and when I press the gas there a slight delay before the car revs. Sort of a hesitation when I accelerate from a stop. The sound only occurs under load and lasts through half a gear then fades only to start again in the next gear. Man I feel like I'm not explaining it well. I have a feeling that its coming from the exhaust system. Maybe a leak in the exhaust manifold, but again I don't see any leaks or burns. If someone can help I'd be grateful cause I'm about to go crazy Thanks. Hopefully Jeff can help me out on another one LOL 😁

MB-Dude

Does your car have ABC and does the noise also have a bit of shutter or subtle vibration when the noise occurs? There is a [damn, can't think of the name] vibration accumulator that is tied to the ABC circuit that prevents this noise/shutter. It is ONLY on ABC-equipped cars. So if you have air suspension, this is not applicable to you.

Otherwise, do you hear the noise when revving the engine and in neutral? If you hear/sense the issue while at a dead-stop and engine revved, the problem is before the transmission planetaries.

Also, listen carefully for an air pump leak. Have someone gently rev the engine while you listen to the various pumps driven by the belt.

And, is the sound a chirp or a burb/fart sound? If more of a chirp, could be an aged belt. If the belt hasn't been changed for a while, consider that. Especially look for the slightest of fraying, cracking, etc.

Cheers,
Jeff

Mrmojo78

Hey Jeff, I have airmatic suspension and I'm sure the noise is not from the suspension. The sound is more of a fart sound and only occurs in drive and while accelerating. I guess I can hear it while in park and reving, but only on the initial push of the pedal.

MB-Dude

Listen closely to your air pump(s) and lines. You probably have something leaking air or a pressure relief valve relieving pressure. I assume the frequency of engine 'flatulence' varies with RPM. Are there any conditions where the sound goes away or is greatly reduced?
Cheers,
Jeff

wallyp

Also check for an exhaust leak. One way to find such a leak is to use a four-foot piece of rubber or plastic tubing. Stick one end in your best ear, use the other end to probe around the pipe on an idling engine. Avoid touching the hot pipe, especially the cats.

MB-Dude

Wally has a good suggestion for listening for leaks and noises in general. Sort of like a stethoscope. I would only suggest adding a short piece of metal tubing on the probing end, just to help prevent melted plastic/rubber on the exhaust system.

A variation is to mix up a tall glass of water with a little dishwashing liquid. With the engine cold and using an old spray bottle that shoots a straight stream, not a conical spray, squirt the soapy water over each exhaust fitting. You don't need much but the fitting needs to be wet. Have an assistant start the engine while you quickly inspect each fitting sprayed. If there is an exhaust leak, bubbles will immediately form as the exhaust gases 'blow bubbles' through the soapy water film.; it will be very evident. Even the smallest of 'pressure' leaks will be found this way.

Do not use this method on a hot engine (liquid simply evaporates and you run the risk of a thermal crack). And do the engine in sections, as the soapy liquid will evaporate quickly as the engine heats up.

Cheers,
Jeff

kraut56

I have a "fart" noise that happens usually within minutes of starting the car.
It is actually a noisy level actuator of the left headlight, which is also annunciated on the MFD as"left beam".

It comes and goes.

markola

hi , I am having the same problem . Were you able to find a solution to it ?