Did you actually switch rear speakers, not just speaker wire? The popping sounds like a speaker issue, not the receiver. Popping is generally produced by clipping, that's to say, over driving the speakers by pumping up the volume from an amp with too little power. This can damage the speaker. Run the mains speaker wire to the surrounds, if you still have popping in the one rear speaker it's a speaker issue, if not, then it's a amplification, amp short produced by heat, or loose connection issue. BTW, if it is the Marantz I would not send to Marantz. I would take it back to the store for an exchange or a store credit. Let the store have the problem. If you bought on line then call the store for a return ticket. I would not use warranty service on a new unit at all. Why should you pay in time or money for a defective product? Also, if it is a receiver defect in the amplification stage, this can damage the speaker if clipping (popping) is excessive.