Car Stereos: engine noise, pioneer deh, loud buzz

Question
ive got noise.does not do it all the time.switched to dedicated ground.seemed to solve problem,opps it started again.engine noise.especially when i turn the lights on and adjust the dimmer then i get a loud buzz through my speakers.1998 toyota camry pioneer deh-p6600 installed using factory amp.its driving me nuts.please help.lol.

Answer
Karl, The usual culprit to this problem is an open circuit, or a non-grounded circuit in the engine compartment.  It is tough to locate and repair.  The best answer, as you have worked on, is to isolate the ground wires that you do know of.  I would make your own ground wires for your electronics.  They should be decent gauge wire, fastened tightly to good metal, and be as short as possible.  Doing this will close your electronics' circuits as soon as possible, so they are not susceptible to the open circuit causing all the noise.  Also, you can buy a noise filter for your power wire, that normalizes your power wire and keeps the rogue circuit noise at bay.  This should be done as a last resort, because they are usually not as effective.  Hope this helps, Scott