Starting a couple of days ago, the bass in my X5 has been going in and out. It is only happening on the passenger side of the truck, and it now goes out more than it stays on. There is no crackling or static noise. It will just cut off and stay off for 5 minutes, turn back on for maybe 20 seconds, then cut back out. Any idea what this could be and what I would need to do to fix? Thanks!