Why does my car stereo cut in and out?

I have a '98 Grand Am. I bought a NAXA NCA-696 deck from amazon.com for about $50. Never heard of the brand, but it has a memory card slot, USB and AUX inputs. But I digress. The unit has performed great up until this point. One day I turned my music up and it starting cutting in and out past volume 30. (fyi: 10 is barely aubible). it seems to be cutting out lower than 30 now. what could be causing this? probably just the cheap discount deck i purchased?