I've had some problems with a crackly left speaker before, but could always seem to clear it with a blast of volume. Now it seems the whole left side is distorted - front and rear speaker. The right channel is very quiet and also a bit distorted. However, when I switch to CD channel and play my iPod it clears and sounds fine. I have had a look at the wiring and couldn't see anything out of place, but to my mind as it is fine on CD channel it must mean the head unit is faulty - ???