Red hi fi tune ups modulating? need help

Last summer I purchased a Red Hi Fi helmet off of NS with the DJ Tune Ups. Now when winter rolls around I start using it, the problem is the audio sounds absolutely horrendous. In many songs the vocals are to quiet to hear or sound like the singer is singing through a fan. Other times the levels are so off that I can only hear rhythm guitar and no lead, bass, drums, or vocals. It also comes and goes like that. I have found that songs with more complex parts and levels sound the worst. My friend who is in recording school listened to it and said the sound is "modulating" . Has anyone else had this problem? SHe was saying that it is a problem with the cable but unlike newer models the cable doesn't unattach from the speakers. I think I will start out by cutting the volume box out and splicing the cable back together. If that doesn't work I will replace the entire cable and resolder it to the speakers unless anyone else knows how to fix this problem.