Amp makes noise. I am purchaseing a new amp
A mono amp will generally provide more power for subs. And for those Audiobahn's, you'll want something that will provide a minimum of 500-600 watts RMS to each, a least a 1000 watt amp. At the low end, something like the Alpine MRP-M1000 or the Orion HCCA-D2400 will provide 1000-1200 watts. I'd recommend the Alpine. For more power, and another $100, look at the Alpine M2000, or for another $250, the Rockford-Fosgate T1500-1bd.
Hope this helps.