If someone out there can answer this question, I'd appreciate it.
Recently, I went to Japan and hooked up an amp (sony) to my girlfriends car stereo (Carrozeria MD-5500? Pioneer). After checking everything and turning it on, I had major feedback and all grounds were ok. I even hooked it up to the battery and still the same. I have hooked up many amps for friends so it's not something I'm new at. It sounds just like a bad grounding problem. I installed it on her friends car and it worked fine so it's not the amp. and I thought maybe it could be the wiring. I installed her friends amp on my girlfriends car and it worked fine!
So, it's not the wiring. I could not figure out why and could not find anything wrong. At last resort, I took it to a stereo shop and THEY couldn't figure it out. If anybody out there has any stereo experience I'd appreciate any responses. I'm going back there in a couple months and I want to finish the job. THANKS !

 

Can you describe the feedback in more detail?

From your description so far, I would say to have a pinched or shorted RCA wire, but I will need more info, such as how it is wired and when it happens?

 

Thanks for the reply.
It sounds like a high pitched buzzing sound. The sound is worse when the engine is running. It's not loud but very annoying. I tried another amp to the car and it's fine so the wires are ok I suppose. When I tried the amp onto her friends car it works fine.
Any idea? Thanks again.