when i push my 4x12 (100W) loudly with my 100W head i can hear the speakers crackle. it's like a high pitch rattle which i used to think were coming from the springs that hold the power tubes in place. are the speakers permanently damaged or is it just the speaker distorting too much? i heard if the speaker is blown there would be no sound out of it and since these speakers are all wired up in series i would know if a speaker is blown out.