Ammonium phosphate... ya know? Fertilizer.
Mix it with water and toss them in, let them soak. What I don't remember (learned this in A&P school) is whether TO or [I]NOT TO do it in a galvanized bucket. I'm leaning toward [I]NOT TO, so try it in a pickle bucket first instead.
Mike Bynum
Another source of the noise to keep in mind is the ringing of the tank itself from the pump vibration. Tap on the tank with your knuckle and listen to the ring. Now, dampen that vibration by grabbing hold of the tank and tap again. You'll have a thud instead of a high frequency ring. I've been...