i am having the same problem for like 2 yrs now and its pissing me off. i do have a zx650.4 as well. im so ready to get rid of it. funny thing is the other day it started cutting off at even at low volume. so than i disconnected the rear spkrs, it doesnt go into protection and cut off now. i started to think its the infiniti spkrs with 2ohm load.