In my 87 300sdl ther is a buzzing sound in the front left speaker when the radio is on and I turn on the head lights. When I move to the rear speakers the sound goes away. I have had problems with the battery going down, when left for a week or so. Is the short in the switch or the radio? Thanks for any help.

Check the radio suppression spring (clip) in the left front steering spindle.

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Thank you, Iam not sure what the spindel is and how to get to it.

Is the buzzing heard while driving, while idling, or with the engine off?

When you say "When I move to the rear speakers the sound goes away," do you mean that you can't hear the buzzing in the rear speaker or that the buzzing in the front speaker goes away?

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
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"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

The sound comes only from the left speaker. It's there with or with the engine running.

your speaker may just be blown.

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82' 300SD

I have exactly the same problem on my '87 300SDL. Not sure which speakers, but I hear hum while sitting in driver's seat when headlights on, battery drains in about a week. Bought car a year ago and mine was this way when I got it. Have not measured the drain or pulled fuses yet. Hope somebody can figure it out.
Can someone explain what "Check the radio suppression spring (clip) in the left front steering spindle." means?

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Joe Myers

'83 300D (light blue)
'82 300TD (off white - parked)
'87 300SDL (silver)

'75 300D (black - sold)
'76 300D (beige - totaled by pizza delivery car)
'82 300D (metalic blue) sold

I'll take a stab at the radio suppression spring comment.

MB, as well as a few other manufacturers, equipped cars with a little spring/clip thing under the wheel bearing cap, in the center of your wheel.
This little clip is stuck in the middle of the spindle once your spindle nut is installed, but before the grease cap is installed. It provides a ground path from the spindle, without having to try to conduct through the bearings.

Weather it actually achieves much, who knows. Most makers seem to have gone away from this practice, but that may be in the interest of cost cutting as much as anything.

Here's a pic of one:

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-Josh
Testing the cheap Mercedes axiom, one bolt at a time...

Some other observations:

The hum is the same loudness regardless of radio volume setting. Same in either radio or cassette mode.

Hum is present without turning key on (i.e. engine off) or car moving if radio on and lights on.

Hum produced when parking lights or headlights on, but not when rotating light switch left for left only or right only parking lights. (not sure what those are really called)

When radio volume turned down, hum seems really loud, but when volume up not very noticeable with radio audio. Especially with highway noise.

Could the circuit that detects burned out bulbs be responsible? Anyone know how it works?

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Joe Myers

'83 300D (light blue)
'82 300TD (off white - parked)
'87 300SDL (silver)

'75 300D (black - sold)
'76 300D (beige - totaled by pizza delivery car)
'82 300D (metalic blue) sold

Good. We can rule out the alternator.

Only the lights affect it? What if you turn the AC/heat blower on with the lights off?
That will determine if its a voltage drop or something coming from the headlight circuit. I would expect the voltage to drop with the blower 'on' just as it would with the headlights. Do this with the engine not running.

You may be on to something, IMHO start at the idiot buzzer that tells you that your lights are on, this circuit doesn't involve the right or left parking light switch.

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85 300CD The FryrBird MY daily driver

The Hazard blinkers and sun roof do not cause the hum. The Hazard blinkers are much brighter than the parking lights, so current draw should be higher. I did not hear any hum with blower on low. The high blower was so noisy I don't think I would have been able to hear it. While glow plug light is on I hear a much lower level hum. That hum stops when the glow plug light goes out. But never heard the louder hum from the glow plugs. I "assume" the glow plugs are still on for at least a few seconds after the light goes out (without starting engine)? So does not appear to be just high current draw. Maybe this will help somebody figure it out.

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Joe Myers

'83 300D (light blue)
'82 300TD (off white - parked)
'87 300SDL (silver)

'75 300D (black - sold)
'76 300D (beige - totaled by pizza delivery car)
'82 300D (metalic blue) sold

Based on this info I'd say it has to be something on the light circuit. Weird.
If you were close I have an O-scope and we could possible track it down.