groaning noise from 560SEL
 

Hello all,
I was wondering if anyone would be able to give me some info on this one.
When I start from a full stop I hear a whining/groaning (like a tiny foghorn?) noise coming from the rear area of the car. It doesn't happen if I start slow, only if I give it a good amount of gas. The noise is more aparent if I start on a steep incline. Once I reach 15-20 mph the noise goes away. The car is an '87 560SEL and there don't seem to be any other symptoms. Any ideas?

Have you pin-pointed which side?

Wheel bearings can groan, dragging brakes can groan, how about a fuel pump (?)

Torque induced grounding out of the trans mount or rear subframe mounts maybe? Maybe torque induced exhaust against the body?

Me likes that idea. :)

It seems to be coming from the passenger side, though it is hard to tell. All four wheels had brake pads and rotors replaced two months ago, so that shouldn't be an issue. Obviously I'll need to have a pro look at it, but I wont really have time until mid January (unless this becomes an emergency issue). I would imagine that it is indeed something torque related (as opposed to rpm), since it does not occur on the highway regardless of rpm.

Just for giggles, next time the car is good an warm check the tranny fluid level. My 4.5 would make a groan/moan once and a while when starting from a stop, sounded like it came from the rear and took forever to pinpoint. Than one day it sounded like it came from the tranny, check the fluid and bigger than Dallas the level was down about 1 pint. Topped up and no more groan/moan.

Your results may be different.

Not sure if this will help but...
My 300 SEL would make a groaning noise when starting off from a complete stop. Turned out the problem was a colapsed motor mount, the motor was sitting so low that part of the exhaust system was rubbing. New motor mounts and now the noise is gone. Just another data point.

Just had the same thing on my 560sel this past summer. With mine - if you bounce the rear bumper - it was really noticable. It was the link to the hydraulic suspension proportioning valve. The link has a universal type pivoting end on it and mine were seizing up. Removing - cleaning off the rust and re-lubing solved the problem. Hope this helps.
Morris