Im running a Carvin ProBass 500 head through a 4 ohm 2x10 cab and an 8 ohm 1x15 cab. When i play at lower levels its fine, but when i turn it up a bit (to like 3 or 4) i get a buzz or rattle(?) from it. I think its coming from the 2x10 but im not sure. Any advice? Also, my cabs say they can handle 400 watts (thats the lower of the two) and I'm only putting out 250 watts at most right now (not bridged). When i cranked it, I thought they would be fine, but they distorted like hell. Why cant a 400 watt cab run cleanly through 250 watts of power? Thanks for any help.