USB Audio problem

I have a Kenwood DPX502BT headunit, and when i use USB, it almost sounds like my speakers are blown, but only on some songs and not all the time, the speakers are brand new ALPINE SPE-6000 6.5in coaxial two-ways. The USB cable is torn pretty badly, but not through the signal cables, so it works fine. however, when i use AUX the speakers sound perfectly fine with no issues, is it possible that because the USB cable is torn around the outside and through the metal coating, which i assume is the ground, that it has affected the sound quality? I am using an iPhone 6 with the original iphone cable. I have not tested the headunit with a different cable. any ideas?