I’ve solved my problem after 3 nights of trouble shooting and wanted to post a brief description that might help someone one day as these problems can be very frustrating.

After my amp blew I replaced it with a 4 channel JBL from my other car that I knew was OK. When I turned the system on the amp stayed in protect mode. Since my amp power and ground connections were already proven I metered out the resistance of my speakers and found that one of my 5.25” woofers was blown. I replaced the speaker.

Now when I turned the system on there was a substantial background hiss with the car off and when the engine was running it was louder with alternator whine.

With RCA’s unplugged and amp turned on there was no noise in system. Amp seems OK. With head unit pulled out of dash and spare RCA’s plugged into HU and run over the back seats to the amp, the noise was still present. Then I plugged my IPod’s 3.5mm stereo jack directly into the amp using the original RCA’s installed in the car and the noise was gone. This showed the HU as the smoking gun. I uninstalled the HU and measured the continuity from the ground pin of the wiring harness to the HU chassis, ground was good. Then checked from the ground pin to the RCA output ground (outer metal sleeve of female RCA connector on HU), there was no continuity and this was my “floating ground” problem.

My fix was easy because I am only using the front and Sub RCA outputs, I had the Rear RCA’s not being used and was able to ground the outer sleeve to the chassis of the HU. This grounded all the RCA connectors as they were connected internally to each other inside the HU.

For good measure because the alternator whine was present I also ran some #4 wire from a bolt that mounted the alternator to the engine to the battery negative and a #4 wire from the battery negative to a new ground on the car frame.

Everything is good now. It seems that when the amp blew it burned up a speaker and screwed up my HU RCA ground connection.

Here’s some background info on my system that had the problem and the amp that caused it all.

System was a Kenwood KIV-BT900, US Acoustic 4 channel amp (USX 4085, bought on craigslist and obviously had a rough life before it got into my hands), Infinity reference components for front stage and JL Audio Subs in the back.

The problem started when the amp blew and sent some funky, loud noises through my system regardless of what I did with the volume ****.

 

It is surprising how common a burnt RCA ground is in headunits. If you have noise, it should be one of the first places to look. Glad you figured it out!