Okay, so recently i got a JBL DCR600 home theatre bundle, its from 2001, but still works great, except the subwoofer. The sub takes about a half hour after being turned on to actually start playing music, and doesnt always work even then, and if i leave the switch on it makes a rumbling noise or randomly starts pumping. I know its not completely broken because when it works it sounds amazing. Its also not the reciever because I tested another sub with it. Is this a common problem? or is it even fixable?