Audio Systems: Car stereo buzzing problem, external amplifier, audio amplifier

Question
Hi Cleggsan,

I have recently had a stereo installed in my car. The problem is that it makes a buzzing sound, the buzzing sound does not increase in level with the volume control, the frequency DOES increase with engine speed and when lights are on it gets louder.  Turn signals and braking make no difference.

I have gone to 3 different audio shops with no answer, though I think there MUST be a solution, since sometimes the buzzing dissapears when headlights are off, so I think that proves that the problem can be solved somehow.

I appreciate your time attention, thanks in advance for any help you can give me.

Regards!

Answer
Does the buzzing go away when the engine is turned off - but headlights are on?
Does the buzz increase if you plug in the cigar lighter like it does when the headlights are on?

I am assuming you have an external amplifier being powered by audio cables coming from the head unit? Is this right?

And, do you hear the buzz equally in all speakers?  

Does the buzz get louder if you turn up the bass control?

I am guessing you have alternator noise getting into the audio amplifier for which you will need to add a filter or replace the alternator in the car.

If you cannot get it resolved, send me the answers to the questions aboe and give me the make, model and year of the car and the make, model and age of the head unit and amplifier installed in the car.

Best wishes,
C