Have you tried a UPS (Uninterruptible Power Supply)? If it's a drop in line voltage that's causing it then that may do the trick.

Keep an eye out, you can usually find them on sale for under $40.

Plus they are better than a plain old line conditioner which can help with over voltage pulses, but can't really do much for under voltage problems.

Unfortunately the problem may not be the actual power. When I first ran my wiring under the floor for my rear speakers they would pop every time the circulator motor came on in my heating system. The wires ran about 10" from the wires to my furnace initially. Moving them about 2' away eliminated that problem. I suspect you are seeing something similar, i.e. not a voltage spike/valley, but an induced signal on the circuit.