Guywith04TL

Ok so I purchased my 2004 Acura TL and it came with an amp, just a few days ago the sound quality is abit off for example when I turn on the car and the volume is at 10 it's ok to hear and then when I turn it up to 15 loud with the base sound but then in a couple of minutes the sound and base sounds like it's at a 10 instead of a 15, anybody have any suggestions? Could it be my speakers or the amp or wiring?? Thankss.