Flapping noises during acceleration - M30

[Adnan]

Hi,

I've noticed for a while that my '91 535 makes a flapping noise during even moderate acceleration. It's pretty evident when the windows are down or the sunroof's open.

It's getting a little embarrasing now as people on the sidewalk turn to look at the source of this odd sound. Any thoughts as to what this might be; intake manifold leak?

Exhaust leak? It sounds like it's coming from the front of the car, not the rear, but it's hard to tell from the driver's seat.

Thanks,
Adnan

[George M]

Hi Adnan,
Actually its clapping not flapping. Bystanders are giving you a standing O for driving such a great car. Sure it is engine related Adnan?...is the clapping in cadence with the engine either by load or RPM. If speed specific, likely a bad tire/displaced belt inside the tire that is making the noise. Believe a bit more information would be in order for a sound arm chair analysis :-)
Cheers.

[Adnan]

Hi George,

True, there's always an appreciative audience but the flapping can be heard even over the sound of clapping.

It's engine dependent, for certain. It is a function of throttle position which means it is load dependent. When it flaps, if I back off on the throttle, the volume decreases. I'm pretty sure that a closed throttle eliminates the sound but perhaps it's still there but I can't hear it. That's why I'm suspecting the manifolds.

Idle is typical M30, lumpy-smooth with a hunting lope that sounds just wonderful standing by an open hood. No flapping then, but load is practically zero.

The trouble is that when they turn to look at the noise, they also notice the bird droppings that are deposited every morning since I park under a tree.

Which reminds me of something I read back in '87 when the market collapsed - "What's the difference between a pigeon and a yuppie? The pigeon can still make a deposit on a new BMW".

Adnan

[George M]

hehehe...good one bro. Well here is a flyer for ya....may be engine mount or trans mount related. Be sure to check your clutch fan and shroud Adnan. As you get on the gas under load, the engine will torque as aging engine and trans mounts yield and you could be quite possibly causing mild contact with the clutch fan into the shroud. Some have reported dreaded clutch fan blade failures either throwing a blade or destroying a stroud with toasted engine and trans mounts that will cause the engine to rotate under load. Not easy to replicate this condition in your driveway as reving the engine will typically not reproduce this interference without load. Check the fan blades and/or shroud for contact with the engine off. If you haven't changed both your engine and trans mounts in some time if ever...maybe your issue.
HTH's and may save your hood if the culprit.

[632 Regal]

might be a loose spark plug or an exhaust leak at the manifold or where the pipes connect to it. Georges scenereo of a bad mount would take presidence in this quest.

[grave77]

I think its the exhaust joint with the outlet manifold I had this problem before the pipe was leaking and this sound like the engine is spitting. but if the sound is louder I guess that u need to take it to an exhaust technican to pinpoint the damaged mufler.

[Adnan]

.

[632 Regal]

MAnn, I think even more heads are gonna roll...

"let the bodies hit the floor"

[632 Regal]

Mann, I think even more heads are gonna roll...

"let the bodies hit the floor"