I've got a brown Fender deluxe amp that I'm using with an old, recently reconed EV SRO. It sounds great, but I notice that the tremelo, when the intensity is anywhere above 5 on the dial, cause the speaker to physically "pump" in and out, even when there's no signal. Is this normal, and should I relax? Or is there the possibility of blowing and ruining my speaker? Thanks!