Speaker pop on amp startup - 1 channel only

I have an amp (Sony TA-N90ES) that makes the left speaker only pop as it comes out of protection. With a VOM I measure about 5VDC on that channel for a split second, quickly diminishing to zero.

I got a very good deal on this amp because of this but I would like to figure out what is going on. Any suggestions? It is a solid state MOSFET amp.

Mark