sooooo...More than likely it IS a bad amplifier..but it could also be something wrong with the deck, or even one of the speakers could have blown and seized up and be grounding out the entire system...The bad thing is very few stereo shops actually do what's in the best interests of the customer, let alone if they even have an employee thats even qualified to work on and trouble shoot electrical systems. Just because they sell and "drop" new headunits into someone's dash doesn't mean squat if they can't pin point issues with a stereo system... So my recommendation is....start with the easiest accessible item and trouble shoot from there. If either of you wants to keep your car "stock" I have everything out of mine (all speakers, tweeters, deck,amp, subs, little children, spare tire..lol)that you can have relatively in-expensively or if you want to replace your stereo with an aftermarket one on your own I'll cut you a screaming deal on a new one!..message me or visit my website and drop me a call
www.soundcreationsaz.com