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  #1  
Old 12-04-2007, 07:25 PM
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Horrible Interference in AUX and AM modes

My 300D has a Blaupunkt Laguna CD36 headunit. As of last night, I have XM radio with a Roady XT receiver, and have it wired up via the AUX connection with power coming from the cig lighter. Now, when the car is on, a whine is present over the speakers. When I'm accelerating, you can hear either the alternator or the turbocharger whining louder with higher RPMs. When I turn on the headlights or use the turn signals, the whine gets worse and more staticy, sometimes accompanied by a ticking if the turn signals are on. It only happens when trying to listen to XM over the AUX connection, or in the rare instance that I'm listening to AM. When I have the car off and the key turned to the ACC position, I can hear XM or AM clearly. Do I need to install some sort of noise cancellation device?
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  #2  
Old 12-04-2007, 07:51 PM
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Check the ground?
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  #3  
Old 12-04-2007, 08:06 PM
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Before all this happened, the radio was having problems that my indy attributed to a bad ground. He relocated the ground and the problems disappeared, so I think this ground is good.
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  #4  
Old 12-04-2007, 08:07 PM
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You running amps?
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  #5  
Old 12-04-2007, 08:13 PM
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Nope, no amps.
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  #6  
Old 12-04-2007, 11:35 PM
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Alright, I'm thinking since the alternator whine is only present when the radio is on AUX or AM mode, and the ground is good, that it may be time to look into one of these http://www.crutchfield.com/App/Product/Item/Main.aspx?g=181150&i=003S25A&search=noise&tp=2653&tab=detailed_info. They also recommend an antenna noise suppresor, though I don't think I'll need that seeing as I won't listen to terrestial radio as much. Thoughts?
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  #7  
Old 12-05-2007, 02:02 AM
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Man, I feel like a newbie tonight posting message after message back to back like this without replies from other members, lol.

I read up and found that on the rear of the alternator, there is a noise suppresor, also called a condensor, p/n: 001-156-69-01. If it gets cracked or damaged, what I've described can result. So, I'm going to take a look at that, and if that's the problem, I can just replace it (I think they're not too expensive fromt the dealer) and be on my way.
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  #8  
Old 12-05-2007, 02:48 AM
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Try your solution first.





I had that problem, and I wound up replacing my headunit.


Fixed the problem, but I was out $$$.
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  #9  
Old 12-05-2007, 09:49 AM
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I was also going to suggest a line filter. Mine has done that before, although the noise level would rise when the engine was idling, not reving.

When you figure out what the solution is, let us know.
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  #10  
Old 12-05-2007, 12:04 PM
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I went out and took a look at the alternator this morning. The condensor is missing. I am thinking that the alternator was replaced by the PO, and as often is the case, the condensor was not swapped, as new alternators do not come with new condensors. I'll be making a trip to the dealer today.
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  #11  
Old 12-05-2007, 02:06 PM
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Check where you're plugged into the cigarette lighter, that's probably where the bad ground is. If there was no problem with radio before, I doubt that the condenser or lack of it is a problem.
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  #12  
Old 12-05-2007, 02:38 PM
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How would you tell? If there's power available through the lighter, what might the problem be?
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  #13  
Old 12-05-2007, 04:40 PM
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Quote:
Originally Posted by hitwtom View Post
Check where you're plugged into the cigarette lighter, that's probably where the bad ground is. If there was no problem with radio before, I doubt that the condenser or lack of it is a problem.
I previously had a Sony unit that would do the same thing on the AM band, so I'm betting the condenser is the problem.
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Sooner or later every car falls apart, ours does it later!
-German Narrator in a MB Promotion Film about the then brand new W123.
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  #14  
Old 12-08-2007, 05:32 PM
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The reason there is whine on aux and AM is that there is multiple grounds and or poor grounds. If one was to take a multimeter and measure the resistance of the grounds of the radio to the battery and the resistance of the grounds to the XM I am sure they are different. Ultimately we want 0 ohms resistance between the radio, XM receiver and the negative post of the battery. I am not talking metal chassis ground but rather negative post of the battery. At the same time if we measure the resistance of the negative post of the battery and the chassis of the vehicle and it is anything but 0 ohms resistance the ground from the battery to chassis must be improved. If the negative battery cable has any green stuff coating the copper wire inside the ground cable it increases resistance and hence all these problems result. All noise problems can be traced to these principles. In short make sure the radio ground and the XM ground have the same 0 resistance to the negative battery post.
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