Hello, I recently got a very clean 1992 240. Automatic with OD

There is a strange bussing that comes from the shifter area under the car while driving. Now it is silent when stopped idling, smooth as glass. When driving it docent seem to correspond with speed at all, bur rather RPM's almost as if it is simply something that it loose matching the resonance frequency of the engine. This does not occur when raving the engine when stopped, only when moving.

What would cause this? the output shaft bushing? carrier baring? perhaps something even simpler than that?

Any help would be greatly appreciated!

 

output shaft is speed based.

rpm based, its more likely an exhaust leak or maybe a broken exhaust hanger near the header, something like that...

 

There is a heat shield on the downpipe right next to the transmission - assuming the downpipe hasn't been replaced (all replacement downpipes don't have the shield, including the ones from Volvo). The heat shield is just in front of the catalytic converter. If it is rattling you can just cut it off.

 

note in California, at least, that heat shield and the warm air duct to the airbox is visually inspected at smog checks.

 

I'm referring to the one underneath the car - not the one on the exhaust manifold. The one under the car is definitely optional as all replacement downpipes come without it. I was thinking it may be the cause of the buzzing since it is right next to the transmission.

 

A have a similar problem with my '90 240. A strange whistling/humming/whining , more like a jet engine coming from below the shifter, mostly at 30-40 mph. Recently, when towed, with engine off, in neutral, that sound was still present. Somebody told me it might be the drive-shaft support bushing and/or center support bearing. I haven't checked yet, my car is at the shop now.

 

Turned out to be exactly that. No more buzzing whatsoever. Found out tho in the last 3 weeks I snapped one of my sway bar end links. Sometimes you just need to relax under your car and just look at things. Thanks for the help guys!