i was gettint that small rumble too...urked the hell outta me.i bought a new amp and i no longer have that issue..is ur amp new or used?

 

The rumble happens sometimes when I turn my car on after letting it sit for a day or more. I don't really care.

 

My amp is used its bean kicking around so I put it to use. On the battery subject again, low water is also caused by an alternatot trying to charge an already bad but not dead battery. On that note my battery was bad, barely started my car on monday. Got a new one and man does that little JL 8 inch sub hit. You would think I have a 10 or a 12 in there. It only has 400 watts going to it. So a bad battery can cause the amp to not get enough power.