Is there a shortage in my radio or speakers?

about three weeks ago i had a car radio put in with new speakers and they had to rewire everything. the car is a 1991 pontiac sunbird LE. It was working perfect the radio was loud and good and then all of a sudden the speakers in the front start going out and only when i turn it down it comes back on. i usually have my radio on 38 but now i cant get it passed 32 without it going out and the rear speakers have also stopped putting out. my base is pretty much gone in the back and i dont know what to do. we paid the people 140 dollars to put the radio in