Hey. I've had 2 Pioneer 10s (tsw-254r) on a Pioneer GMD-9601 amp for about 2 weeks. The subs were wired to 2 ohms when I had only had 2 of them and they sounded fine. The amp is rated for 800w rms @2 ohms. ( The subs are rated for 250w rms each) and I added 2 more of the same 10s so I have 4 10s total. When I added the other 2 I wired them to 1 ohm (amp is rated for 1200w rms @ 1 ohm) so each sub is on about 300w rms. 2 of the subs are brand new just got them today from SonicElectrinics. The gain is about 1/8 to 1/4 of the way up(same place as it was when I had 2 10s) and now one of the brand new subs makes a really nasty loud crack or crackling sound when you turn the volume up high or turn the bass boost knob over about half way. I think it's only 1 sub making the sound but I'm not sure. Do y'all have any idea what it could be? Thanks for any help.