Headlights cause hum with aftermarket head unit

[wago]

Okay, so here's a strange one. I just installed a Kenwood DDX5120 head unit in my '06 A4, and I'm getting a hum whenever the parking lights or headlights are on. No hum when the lights are off.

The deck is wired to the factory harness (Bose amp, etc) using the metra adapters. Do I need to run a new ground wire? Add some kind of filter on the 12v DC input to the deck?

This is strange, since I installed the exact same deck in my wife's B6 avant a few months ago, and she doesn't have this problem. She doesn't have Bose, tho...

Anyone seen (well, heard...) this before? Thanks!

[Sanjman]

sounds like you aren't properly grounded... check your ground wire and make sure it is connected to a good strong ground (usually a screw you can find inside). Is there a ground cable included with your unit?

[wago]

Yeah, I just used the factory ground from the wire harness -- I didn't run another ground wire to a bolt or anything. I'll give that a shot. Just strange that it only happens when the parking lights are on...

[Quattro]

who hooked it up? Could be ground or when you tapped into a wire for the light on the unit its creating a problem.

[airbornerifleman]

I get the same hum when I turn my lights on, but I only hooked an amp and a couple of subs to the stock Symphony 2 head unit. I got it all done professionally.

[Asimko]

If you hooked up the orange illumination wire just disconnect it and cap it off. That wire is not needed for the deck too work. If that does not work try running your own ground. Also make sure all the wires are seated in the harness properly.

[yettavr6]

Just installed my Pioneer and im getting the same hum. very frustrating. I didnt have any problems like this with the pioneer in my jetta. I haven't tried disconnecting the illum wire yet, but that wont really solve the problem as that is pretty much needed on a nav unit (to dim the screen and switch the map to night colors). I also used the ground from the factory harness.

[a4dc89]

its called a ground loop and a new ground wire usually does the trick with some added shielding of course

[wago]

Just installed my Pioneer and im getting the same hum. very frustrating. I didnt have any problems like this with the pioneer in my jetta. I haven't tried disconnecting the illum wire yet, but that wont really solve the problem as that is pretty much needed on a nav unit (to dim the screen and switch the map to night colors). I also used the ground from the factory harness.

Does your deck actually dim when you turn on the lights? One of the things I noticed is that the Kenwood nav unit doesn't actually dim with the lights, even though I connected the orange dimming wire through the harness. Do the B7 cars even send dimming voltage, or is it all CAN-bus these days?

[yettavr6]

Yes, it dims, and im convinced there is no fix for this. I've tried grounding the chasis of the HU (using the bolt on the back), grounding the RCA's, and disconnected the illumination wire. Nothing helped, and in fact grounding the RCA's made it louder. It amazes me that the factory headunit would have better noise isolation then a "high-end" aftermarket headunit. Leave it to Audi...

[yettavr6]

Just curious who else that is having this problem has Bose? I think it may be something to do with the amp itself. I used this harness to connect the Bose amp to the low level outputs on the Pioneer. If i unplug all 4 RCAs from HU, the noise goes away, but if i unplug only 2 (or 1 or 3) then the noise is even louder than with all 4 connected.

[bcramer]

Just curious who else that is having this problem has Bose? I think it may be something to do with the amp itself. I used this harness to connect the Bose amp to the low level outputs on the Pioneer. If i unplug all 4 RCAs from HU, the noise goes away, but if i unplug only 2 (or 1 or 3) then the noise is even louder than with all 4 connected.

Here you go.

Troubleshooting Noise
Noise is a very common problem that plages a lot of people and can be a real pain to troubleshoot. Typically noise only happens with systems with an amplifier. If you have noise and no amp, your head unit is at fault and you shold reground it.

Steps to solving noise:
1) Set boost to 0 and your gains using this guide here
2) unplug the rcas from the amplifier.
- if noise doesn't stop, reground the amplifier
- if noise doesn't stop, unplug speaker wires one at a time (leave power wires), the wire with a short will will stop the noise when you unplug it
3) If noise stops:
- replace the rcas
- if noise doesn't stop, reground the head unit
- if noise doesn't stop, ground the rcas (strip about three inches of wire and wrap it around the outside metal of the rca connectors, then run to the screw on the back of the head unit
- if noise doesn't stop, replace the head unit

Pionneer units are KNOWN for having the ground trace blow out, which requires you to ground the rcas. Having the nub in the middle of the rcas short out will also blow the ground trace either completely killing the rcas, or blowing the ground trace.

Still have noise and the steps don't work? Try this:
take a piece of wire (most wire comes in pairs - handy). Strip about three inches from each wire at one end. Wrap the wire around the outer metal part of the rcas at the head unit end - this part is called the barrel or jacket. Next, tape the wire in place. Finally, connect the other end of the wire to a good solid ground. One of the screws on the back of the head unit works nicely, as well as the same place you grounded the head unit.

You should never use a ground loop isolator. If you have noise, you have a problem and should address it accordingly.

[yettavr6]

Yea i've tried all those steps already, so really my only option left is a ground loop isolator for the RCA's. I'm gonna order two in a few minutes.

[bcramer]

Yea i've tried all those steps already, so really my only option left is a ground loop isolator for the RCA's. I'm gonna order two in a few minutes.

Bummer.

It's probably being induced by the Bose amp then. Have you checked all the OEM grounds to make sure that they're still good and nothing has corroded?

[Geoffafa]

it happens to me too, ijust turn up the music, kinda the reason i got the unit in the first place.... to play music louder and clearer then the OEM headunit

[yettavr6]

Today i tried two different things:

ipod connected to the Bose amp: no hum

preouts on HU connected to a set of PC speakers: no hum, even with speaker volume on max

I'm going to try using THIS instead of the preouts on the pioneer.

One reviewer said this which makes me think it will solve the problem:

Problem: Getting aftermarket head units to play nicely with 98' E320 stock Bose amplifier. Line out from aftermarket HU to Bose amp and you get a nasty thump when source is changed or volume turned to zero. I thought it was a flaw in the Alpine receiver. On to a new Pioneer DEH-P5000UB for bluetooth purposes (awesome!). I found the same problems. Also tried speaker out to factory amp but that option came with other issues like 'one click, too loud' and hissing on soft tracks. The Scosche SLC4 knocked these problems square out. Easy to connect. Adjustments were puzzeling. I just set all channels equal at half mark and set the mode switch to what sounded best. It delivered what Bose was looking for. 5 clicks into the volume and the sound increases nicely and has a solid full range as I continue to increase the knob. No clicks, pops or hissing!

[yettavr6]

Just wanted to update you guys. I bought that line level converter and installed it yesterday.... no more hum! Sounds better overall too.

[wago]

Thanks to yettavr6 above, I installed the Scosche SLC4 this weekend as well, worked great. The headlight hum is nearly gone. I used the RCA outputs to feed the signal to the bose amp. I also had to use an adhesive cable tie mount and a couple zip ties to firmly attach the line-level inputs to the Scosche. As some reviewers have mentioned, the Scosche line-level input screw terminals don't hold the wires very well.

[Dimon]

Today i tried two different things:

ipod connected to the Bose amp: no hum

preouts on HU connected to a set of PC speakers: no hum, even with speaker volume on max

I'm going to try using THIS instead of the preouts on the pioneer.

One reviewer said this which makes me think it will solve the problem:

Ohh yeah I found what i need!!

[mec]

humming? strange, just buy my headlights in the classifieds section :)