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Old 10-18-2014, 01:12 AM   #1
CapBackfire
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Constant Hiss

I have a constant hiss coming from the left footwell in my 2004 325Ci with HK ever since I installed my GM5150. I believe I'm using the 40-pin connector. I cannot figure what is causing it.

I have found that:
- The hissing fades out as I increase the throttle, but then it will fade back in
- It's not related to the amp, I unplugged it and the hiss persists.
- The hissing only comes on if the engine is running, it's noise free in just the accessory.


Here's a 30 second video I took as a sample. At first the engine is running and you can hear the hissing. I turn it off, move to accessory and you can hear that it's gone.


I've searched the forum, double checked the Eonon GM5150 threads, and checked to see if it was just picking up noise from nearby wires but in all I've found nothing. Any suggestions? could it be as simple as grounding?

Edit: I edited the title. I've concluded it's not the head unit causing the hiss.

Last edited by CapBackfire; 01-24-2015 at 03:56 AM. Reason: clarity/update
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Old 10-29-2014, 01:42 AM   #2
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Old 11-14-2014, 06:16 PM   #3
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Update! (I guess). After going through some trouble-shooting with Carlos of Eonon we determined the hissing is not due to the head unit. Hopefully I can find an exact cause this weekend.
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Old 01-24-2015, 04:02 AM   #4
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The hissing continues. I plan on checking out the amp this weekend. Has anyone experienced something like this before? To clarify the symptoms are:

- Hissing towards the front left speakers while engine is running.
- Audio sounds normal/hiss free when the key is just in the accessory.
- When accelerating/putting load on the engine the hiss begins to fade, eventually fading back when there is less load on the engine. If I put it in neutral and rev it up the hissing does not fade.
- Turning off or unplugging the head unit off does not fix it.

Any suggestions or directions to other threads are greatly appreciated.
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Old 01-24-2015, 04:16 AM   #5
Gatriel
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Sounds to me like alternator whine, due to a bad ground.

I would double check all your grounds, especially with the newly installed hardware. Make sure the grounds are grounded directly to the chassis, and are as short as possible.
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Old 01-24-2015, 04:26 AM   #6
CapBackfire
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It's unlike any alternator whine I've heard, more of a "ssssssssssssssssss" than "whiiiiiiiiiiiiiir".
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Old 01-24-2015, 05:01 AM   #7
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Quote:
Originally Posted by CapBackfire View Post
It's unlike any alternator whine I've heard, more of a "ssssssssssssssssss" than "whiiiiiiiiiiiiiir".
So its more of a white noise then?
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Old 01-25-2015, 01:25 PM   #8
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Yes. It's present in the video of my original post. I've had alternator whine in my old car, this doesn't seem like it. Though I'm going to see about grounding it because it's clearly related to when the engine is also running.
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Old 01-25-2015, 02:02 PM   #9
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Quote:
Originally Posted by CapBackfire View Post
Yes. It's present in the video of my original post. I've had alternator whine in my old car, this doesn't seem like it. Though I'm going to see about grounding it because it's clearly related to when the engine is also running.
I remember back in the day at CarToys when we'd experience this with 4 channel amps, we'd run RCAs on one side of the car and power on the other side, and it tended to help, but this is a completely different situation.

When you installed your GM5150 -- did you have OEM nav with the long wiring harness?

If you did, I would chassis ground the unit, and then give that a shot.

The noise could also be coming from your fuel pump -- but if you had the long wiring hardness I cannot imagine you running the 17' extension cable on the passenger side.

Also your video is marked as private, so I cannot listen to it.
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Old 01-25-2015, 02:10 PM   #10
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http://forum.e46fanatics.com/showthr...cuum+leak+dash
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Old 01-26-2015, 12:48 AM   #11
CapBackfire
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Sorry about that, I changed it to unlisted o it should be viewable.

No, I had the business CD unit that came stock. Im not sure which connector I have. It's a 2004 so tht should be the 40? The only nonstock piece of hardware is the gm5150, but it persists when the head unit is unplugged.

Invisible man- thanks for the vaccum leak thread! It makes sense as the hissing fades back as engine load eases off, when the mpg gauge would be moving.
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