I just installed a F900BT is a 2008 Audi A4, and i get a severe huming/buzzing sound whenever the headlights are on. My car has the Bose system and i usedthis harnessto connect it to the Pioneer. From searching I have tried the following with no luck:

-Tried 2 new grounds for the HU, on different sides of the dash (no difference)

-Tried grounding the chasis of the HU (no difference)

-Tried grounding the RCA's (noise got even louder)

-Disconnected the illumination wire (no difference)

If i disconnect 1-3 of the RCA's from the harness, the noise more than doubles in volume. If i disconnect all 4 the noise stops. I'm really at a loss here and would appreciate any advice. The only other thing i can think to try is some RCA ground loop isolators like these but I'm not sure which kind i should get. I dont mind spending a little more if it will give me a cleaner signal.

P.S.

I know this is not F-series specific but the vehicle specific board is pretty dead.

Are you using the RCA connectors of the harness you provided the link to?

There are specific RCA connectors that come in the box, try connecting them instead.

i connected the RCAs on the harness i linked to the RCAs on the white pioneer harness

Can anyone suggest a good ground loop isolator? I'm seeing several different brands (metra, sosche, PAC, Xitel), some are cylinders and some are squares, and then i also noticed that some have one or two ground wires, while others have only the RCA connections. I have to wonder if the ones with ground wires are just a pretty way of doing what i already did by grounding the barrel of the RCA. I want to make sure i get one that has some actual circuitry inside to filter out this damned noise. I also don't really have any ground points close to the radio, i would need to run a wire over to the kick panel on either side. If no one has a recommendation I guess I'll try the one that BestBuy sells. I forget the brand, but it is one of the ones that has 2 ground wires on it. At least if i get it there and it doesnt work i can return it Damn you ground loop, damn you.

i think maybe you should try just connecting the speaker leads directly instead of using rcas. the 700 and 900 both have very weak preout voltage...about 2 volts. the 90bt, however, has 4 volt preouts which are much better in eliminating noise interference.

so maybe give that a shot and see if it works. you may need to pick up a different harness though that has speaker leads instead of rcas.

Yea i'm thinking about trying that too, but i think that will overpower the amp. on my jetta i connected the monsoon amp directly to the speaker outputs on my D3, and the key beeps and navi voice were always too loud. I guess it would be worth it though to get rid of this noise, and i can always just delete the key beep.

Thanks for the advice!

Although the last thing i need is one more box to stuff in my dash, i may try this too:

http://www.crutchfield.com/App/Product/ ... C4&tp=2001

One review for this product:

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!