Was cruising along listening to some Hucci via my JVC KD-X320BTS head unit. It's at 80% volume which the setup has had no noticeable issues performing at before. Then the sub tanks and starts rattling. I need to get a new one, but have no idea what specs to get. (Not going to replace the stock amp, though; amp is essentially dedicated to powering the sub because my HU powers the other speakers.)

Is 8" correct?
What RMS/Peak wattage should I get?
What impedance?
Other advice?