thats very odd. my only guess is that its pulling to much power and cutting out. maybe at high volume a very weak signal voltage is causing the deck to clip, or something to that sort. its definetly a deck problem though, it needs to be repaired or replaced.
sony stuff works, no doubt, some like it. it lasts some times, most times it doesnt though. they use cheap parts to build their products, and thus they sell them cheaper. they put 3000 WATTS MAX POWER!!! on their boxes, to fool those that dont know basic fundamentals of electricty or cars. their brand name sells to everyone that is unknowing of their practices. yes sony makes some very other good things though. i own many sony products that work very well and have lasted a long time. the only thing i question of sony is the integrity of their car audio products. some times it affects what i buy when their are comparisons with other sony products, but not all the time.
just thought i'd clarify my opinion on sony.