When the old alt. seized up? If it was you could have worn the belt enough to cause this problem. Or if the belt has stretched to much this will also cause this to happen. I had that happen on my old car. Another thing to check is the belt tensioner. It should be really hard to push down. Also check the rest of the pullys to make sure they all move freelly (exept for the one on the crankshaft of course ) And of course last but not least, check ALL connections.