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I recently got a 2006 Mercedes e350, passed it's Mercedes certified check up a week ago so it's electrical should all be in working order.

The last couple days I noticed the volume of the sound system randomly rises/falls in odd cycles. It fades up and down, sometimes almost inaudible, other times way too loud. Adjusting the volume when it drops/rises just means the next "cycle" will be even more inaudible/ear splitting. It's happened consistently for the last two days; best I can recall it never happened before then.

I'm not accidentally hitting the volume buttons on the wheel and the volume knob on the main console stays firm. Both the buttons and the knob work fine, and I've reset the sound system to default settings a few times. There's no other settings (that I can tell or saw in the manual) that would affect my sound.

The problem has been with playing CDs, the Radio and the Aux input jack, so it's all sound.

What would cause this and how can I fix it?

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  • Is this sort of question on topic? It's not about the engine which the FAQ stresses but I saw lots of other questions about alarms/ect. Is there a better tag than electrical for this sort of problem? – Ben Brocka May 18 '12 at 3:52
  • The general rule of thumb tends to be "would you take it to a mechanic or automotive specialist if you couldn't fix it yourself" - you would with an electrical problem so I'd say this was on topic. I've added 'radio' and 'audio' tags. – Nick C♦ May 18 '12 at 8:52
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    Are the speedometer and cruise control working normally?Many radios are sync'ed to speed monitors to adjust radio volume as speed increases.If your radio has this function it might have switch or settings to diable it.That would help isolate it to a radio or control problem.I have heard of cases where swapping the radio actually disabled the cruise control. – mikes May 18 '12 at 10:45
  • @mikes speedometer's working right, haven't checked the cruise since last week but it was working fine (don't use it in my daily commute). I'll double check for settings related to that though, I thought it might be some feature like that (louder when there's more engine noise...not that it has much engine noise) – Ben Brocka May 18 '12 at 13:09
  • Actually I know the analog speedometer's right, I'll double check that the digital speedo reads the same thing – Ben Brocka May 18 '12 at 13:53
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Have you tried making sure that, for all your speakers in the car, the wire that hooks into the back of them could be loose and could be wiggling around when driving and causing it to go from bad to good connection which would cause the problem you're having. I had this same exact problem in my Honda Civic

Also, have you made sure that all your speakers are still good? If one is blown it could cause this ( not all blown speakers make that constient annoying sound some will fade in and out for a while until finally giving out all together ), and if its just giving out on you or going bad, they will normally fade in or out or quit on you instantly or make that annoying sound constantly. When you check your speaker wire, even if it is firmly still in your outputs follow the wire all the way to your speaker and make sure you're not getting a bad connection from a damaged wire.

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I would check the alternator or you might have to change the battery, I notice that I had that problem. And once I changed my battery the problem went away. I believe it is a voltage drop which causes the volume to drop.

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