I believe I know the problem. The RF punch 400 (assuming you have the 2 channel model) is not stable at 2Ω in bridged mode (running one sub). It is rated at 400 watts RMS at 4Ω bridged which is adequate power for this sub and the enclosure you specified. But if you do have a single voice coil 2Ω sub you should not use that amp to power it (I did not know that alpine type R subs were available in single 2Ω variety, mine is a dual 2Ω sub). If you do have the dual 2Ω variety be sure it is wired in series not in parallel. If your sub and amp are not matched that is what is causing the distorted sound. My sub/amp combo sounds great. It does not pound out my fillings but I do get crisp deep bass out of it. See amp specs here. See sub specs here.