One of our older systems used to have a similar problem with the sleep function - basically if it wasn't getting "enough" signal coming in it would go into sleep mode, maybe turning up the sub output on the amp and turning the sub itself down would help. With regard to the popping, that's reasonably normal, it's just a power up/down thing, shouldn't be anything to worry about - in-fact the previous possible solution with the volume would probably lessen than too!