I had something like that happen once….the clipping and more bass at lower volumes….and it ended up being that the amp was bad. It was a brand new Rockford Fosgate….I’m a big Fosgate fan and usually have at least one of their products in all of my vehicles….which I installed for someone else. But like Audiobaun stated, it could be any number of things and, especially without being there in person, we could throw suggestions at you all day. I too would bring it back to the shop for further testing.