Car audio/subwoofer problems

Recently I encountered a problem after having someone install my subwoofer for me where the audio will randomly cut out of all speakers but the subwoofer. When this happens the subwoofer plays all of the cars audio but only the bass sounds clear and the rest of the frequencies sound muffled and almost like it’s underwater. This happens usually every day where I’ll get maybe twenty minutes of normal music and then it will cut out. Oddly enough if I open and shut the rear driver side door or press the car unlock/lock all doors button it will sometimes kick back on temporarily. I’m pretty sure it’s not a ground issue as I’ve checked and the ground wire is tightly pressed against the bottom of the car. Any help or advice would be greatly appreciated as I cannot get into the shop until next week and would prefer to fix it myself. Thank you!