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      02-17-2012, 11:28 PM   #1
Adam135
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Question Noise/hiss coming only from rear speakers

I'm getting noise or static from the rear speakers in my 2009 135i coupe. I have the base stereo system without iDrive. I did a search and found a couple people with similar symptoms, but I haven't seen what causes it. The signal coming from the amp is clean, the speakers are picking up interference somehow. The noise remains when the speakers are connected to an external amplifier. Anyone know what the deal is, or how to fix it? I'm taking it to the dealer next week but it would be nice if I knew more information ahead of time. I bought the car used, according to service history it has had 4 TSBs performed.
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      05-09-2012, 09:59 AM   #2
wjp007
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Get this. I had the same problem. Mine would come and go. I found that when I inserted a CD, I would get a whirring noise when the CD would start to play (even if the volume was all the way down). Having lived with it for a month or so, I decided to take it to the dealer. While driving I started thinking about what could be causing the problem. For me the sound was there even if the radio was off. So I though this must be some interference being picked up on the wire from the head unit to the amp or the ground connection missing. Possible causes could be the ground wire not being connected between the head unit and the amp, or the wiring harness shield not being properly grounded. So I thought maybe it's a loose connector at the back of the head unit. So while driving to the dealer I decided to try the extreme technical solution of giving the head unit a whack with my hand. WTF, it worked! The noise went away. Nothing but silence coming out of the speakers and the music from the radio. How am I going to explain this to the service manager? I left the car anyway. Let's see what happens. It's clear that it's a faulty connector in the back of the head unit. If your wondering, I hit the face of the dash just to the right of the head unit with the base of my hand. Unbelievable.
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      05-09-2012, 11:03 AM   #3
Adam135
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Huh... weird.
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      05-09-2012, 11:58 AM   #4
entendu
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Any chance it's a cell phone? Try taking a drive while leaving your phone at home and see if it still hisses.
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      05-09-2012, 12:40 PM   #5
wjp007
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No, not the cell phone. I'm an electrical engineer who used to design cell phones. I know the sound which comes from the radio transmission being demodulated into the audio band. This is clearly interference from the electrical components of the car. I notice an buzzing sound when I step on the brakes. If it were the cellphone, the sound would change as you move the phone around. Also the sound should change when you place a call. These symptoms don't happen to me. I'm convinced it's a loose ground connection on the wiring harness for the head unit.
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      05-09-2012, 01:12 PM   #6
bmw1racer
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Quote:
Originally Posted by wjp007 View Post
So while driving to the dealer I decided to try the extreme technical solution of giving the head unit a whack with my hand. WTF, it worked! The noise went away. Nothing but silence coming out of the speakers and the music from the radio.
LOL, that's old school electronics repair that you'd do with electronic tube equipment...

(BTW, I'm a EE as well. )
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      05-09-2012, 09:07 PM   #7
entendu
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Quote:
Originally Posted by wjp007 View Post
I'm an electrical engineer... I'm convinced it's a loose ground connection on the wiring harness for the head unit.
Didn't they teach you to test and not assume? :P
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      05-10-2012, 05:35 PM   #8
TMR013
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Had this happen to me a couple times. completely random. Never did figure it out but it hasn't happened in a long time now
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      05-11-2012, 01:08 PM   #9
wjp007
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I just got my car back from service. They replaced the head unit (for the display cutting out when it's hot issue). Hopefully this will be the last of the hiss/white noise issue.

If it does happen to anyone, don't be afraid to give it a good whack Seriously though try taking out the head unit and checking the connectors. I am convinced that this was my issue.

BTW, this problem started after I had my radio firmware updated by the dealer. I had an issue where no sound would come out of the stereo. I had to power the car off to get the sound back. Either the main sound connector was never seated properly when the units was put back in the dash, or the connector has a faulty design.
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