MTX 1501d + 8500 twin 15 clipping?

Amp is not hot at all. (2) DVC 15" 8500 4 OHM subs, with voice coils wired in series, and speakers wired in Parallel. Each speaker is connected to one of the 2 mono speaker plugs on this amp. Gain is set to about 70-75%, when I up the SW level on the Alpine HU, I hear a POP at high levels. These are used speakers off Ebay. The subs sound good at about 1/2 voulume. The car lights are not flickering at all at high volume, wired with 4 AWG and Bosh 125 amp alternater. I don't think it is a power thing, as the lights are'nt flickering, and the amp does not get hot. This is the MTX 1501D, a class "D" amp. Are these speakers blown, is this the limit of the system, or is the clipping circuit on the 1501D amp working to conservatively--and I am just hearing the "clipped" sound at about 3/4 gain, and 2/3 volume(SW level on HU)? Or ?

Dude TURN DOWN THE GAIN. It's not a volume control! With it 3/4 up it could be clipping really bad. Especially if your deck has high voltage preamp outputs. Do a search on settings amplifier gain on this forum and you will find alot of information about it. JL audio's website has a good tutorial on it also.

Yes. Learn what gain is and how to set it. IT IS NOT A VOLUME CONTROL!New Project: 2003 Pathfinder