Buzzing noise from 560SL

[loubapache]

I have the same noise and a few of my friends also have it. One of them had it when the car was new and it got a bit louder as the car ages.

The noise sounds almost like a small jet airplane taking off and I have had over 60k miles on that noise now.

Anyway, I think the noise does come from the rear differential and there are two possible explanations (neither is a big deal except to the ears):

1. There is a slight mis-alignment in the differential gears.

2. The differential might be too close to the rear sub-frame mount that it might touch it.

Bo

If the buzzing noise sounds like it is from the right rear of the
560SL, it is most likely one of the two electric fuel pumps. When
the fuel pumps get to their service life they will make this noise.
The way to diagnose this is to have the car motor running with
the transmission in park, get a narrow stick about 24 to 36 inches
( I mean 75 centimeters) long, look under the rear of the right
rear tire to locate the two electric fuel pumps and the fuel
filter canister (all colocated to the right side of the fuel tank.
Place one end of the stick on either of the electric fuel pumps
and place the other end of the stick flat against your ear. The noise will be loudest on the failing fuel pump and you will know which pump needs replacement.
When one of the pumps is failing it will be noiser when the fuel
flow is needed to be greater such as when you press the
accelerator.

The other cause of the noise when you accelerate can come from
loose bolts on one of the rubber flex disks located on the
driveshaft either immediately behind the transimission (most likely
if the transmission has been removed and replaced) or in front
of the differential. If the bolts and washers were installed incorrectly (the washer must be under the nuts with the washer
on the rubber flex disk and not the bolt heads, the bolt heads should be against the metal flange ) they will loosen up and cause the noise when the drivetrain is under load. No washers should be between the bolt head surface and the metal flange.
Washers should go between the rubber flex disk surface and the nuts on the end of the bolts..... Needless to say all six of the
bolts need to be (uniformly) really tight on both flexdisks so use a torque wrench....

In my post yesterday I forgot to talk about another source of
noise in the '87 560SL... I had to replace both motor mounts
since they had both failed. When the mounts fail they allow
the engine to drop onto the front subframe and the noise will
be noticably louder. The way to tell if the mounts are failed is
to look under the front of the car an see if the bottom surface
of the aluminum oil pan is below the bottom of the subframe.
The oil pan bottom surface ( has ridges approximately 2 or 3 centimeters apart and run from front to rear) should be above the bottom surface of the front subframe. In fact the subframe
is supposed to protect the fragile aluminum oil pan from
making contact with anything passing under the car.
Seeing the bottom surface of the oil pan is definitely a sign
that the engine mounts are failed and this will be the cause of
an increased noise level in the car. In any event the '87
motor mounts are at their service life and should be replaced.
In any event if you see either side of the oil pan bottom surface below the subframe you are risking a $900.00 ( plus labor ) oil
pan on a chance bump into a parking stop or curb......

See my other post (yesterday) for the source of buzzing from the
rear of the 560SL.

Thanks for your feedback. The noise that I am referring to is more like a humming noise than buzzing. It comes around the speed of 15 miles and stays as I speed up. Once I take my foot of the gas, it goes away. As soon as I push on the gas it comes back. It is very difficult for me to pinpoint the exact location of the source of the noise. As far as the engine mounts are concerned, I will have them looked at. So far, I have shown my car to three mechanics and they all said that the subframe mounts are in good shape. With the top down, I cannot notice the noise. I notice it mainly with the tope up and windows closed. The car is really tight. I am still not happy about the suspension. I expected a much comfortable ride after I replaced all the four shock absorbents. You know, I wish I could find a mechanic I could really trust.

Regards,
Abe

[jkazzoun]

Any chance it could be the fan? Mine makes a certain noise that I would describe as whining more than a buzzing. It only happens when the car is warming up. Someone told me the fan was not off, but not at full speed either and it makes noise at this range.

Am I making any sense? Does this ring any bells for anyone?

[jkazzoun]

Any chance it could be the fan? Mine makes a certain noise that I would describe as whining more than a buzzing. It only happens when the car is warming up. Someone told me the fan was not off, but not at full speed either and it makes noise at this range.

Am I making any sense? Does this ring any bells for anyone?

[The Black Guy]

Joe,

You may be right. I have a 380 SL which makes the same sound when warming up. Almost like a mini supercharge whining sound. Once warmed up, the whining sound goes away.

Just a thought.

[jkazzoun]

Mine does it when warm sometimes as well. Like this am. I think I got used to the noise but after posting on this thread I started thinking about it again. I'm having it checked out next week. I'll report back. The shop I'm going to is a German family that only does MB and should know. They have 3-4 late model 107's in there at any given time.

The fuel pump thing sounds logical as well.