I have exactly the same situation: I installed JL XD 600/6 with Technic's harness. There is a hissing noise all the time (radio turned on at 0 volume or turned off altogether).
What I have tried:
- I unplugged all the RCA cables and the hissing noise is still there. Also when I plug them in one by one the hissing noise is audible on all speakers.
- the gains on the amp are set at minimum on all channels - the hissing noise is still there
- I sanded the tip of the ground cable and connected it back to its location ( above the amplifier on the left side) - the hissing noise is still there
- I changed the High-pass to Low-pass to None and still the hissing noise is there, but with a slight different tonality (it sounds just a little bit different)
- the only time when the hissing noise disappears is when the amplifier is turned off.
Could this be caused by a bad amp because I am running out of options?
Notes:
- I have a 2009 335i with HIFI stereo - for now I still have the original speakers, the only change is the JL amp.
- for the installation I followed exactly the steps from this link:
http://www.the9thyard.com/2012/03/e9...o-upgrade.html
Any advice is highly appreciated!