friend has system problem

A friend of mine is having an odd problem of his bass going out whenever the car comes to a complete stop...could it be because his subs are being run off his stock amplifier?..its a 97 lincon continental and i know it sounds wierd but i promise he's runnin 2 mtx 10's off of it and really hasn't had any problems till now. So anyone know of problems like this?

I personally haven't taken a look at his stuff yet..he tells me when hes at a complete stop..there is no bass..but when he starts moving again it starts back up..wierd..i need to take a look at it but keep the replies coming.

Check to see if the alternator belt has gone bad.  Or maybe the alternator is dying.  When a car is idling, an alternator puts out minimal voltage.  When an engine speeds up, the alternator voltage output goes up.  Could be the amp is shutting down on low voltage.  Next time he is stopped and the bass "goes out," put the car in neutral and rev the engine.  If it comes back on, I'll bet you a nickel it's either a bad alternator, bad voltage regulator, or bad belt.

It's def. not an alternator problem because he just replaced it maybe 2 months ago. As for the alternator belt..i dont even know where thats located or how to check if its gone bad..but i'm guessing with a new alternator it hasn't..could it be the low power the amp puts out is not enough to run the subs at low voltage..although he's been running them fine until now. Maybe it just started to crap out?