Audio Systems: sound system cutting in and out, dashboard area, lincoln aviator

Question
I have a 2004 Lincoln Aviator and recently the speakers cut in and out, really fade in and out. My stereo is a 6 CD changer, radio and it is labeled Sound mark.  I believe it is a 7 speaker system.  Thank you so much for your time.

Answer
Question:  
Does it do this on AM radio?  FM radio?  CD?
Do all speakers fade out or just front?  or rear?

If on radio listening only it is likely an antenna problem such as the power up is not working all the way or the grounding of the antenna is getting rusty underneath where the cable comes in to the dashboard area.

If the fading in and out is with all sources including cd the problem is electronic and could be in the head unit or in the power amplifiers that are mounted elsewhere in the vehicle.

It should be looked at by a qualified technician who can diagnose it through a testing method.  The best people to look at these kinds of problems are usually found at private install/repair shops in your area.  The Lincoln car dealer will probably not be much help unless they have an electronics specialist on staff - and very few of them do - nor will a chain store like BestBuy be able to help much.  

Maybe this will help you get the right solution.