My 04 has the exact same issue. At around Vol25 it would start to pop the same way. I figured I just blew the speakers. If you look at the size of the magnet on those speakers, it is relatively small = craptacular, meaning it cannot handle bass well. I am just waiting on my Alpine upgrades to come and it should get rid of this issue. A pair of aftermarket 6x9 speakers should solve the issue.