Help Please Woofer Pumping Is it Amp, CD or ?

there is a slight crackling barely audible in the signal

Sounds like a a component is giving up: could be a cap... OR you have a very bad connection s/where. Very strange -- any technicians close by to check yr amp out?

Thanks for your responses. I emailed with Michael Elliot, the original designer, who stated that a surge of up to 10 volts (12.5 watts) at power up and down is normal. I measured that, and came with well under 5 volts...no problem, and even between speakers. The worse part has still to be resolved. The right channel has a diminished output signal usually, and there is a slight crackling barely audible in the signal. The problem as I discovered today testing everything independantly is most definitely the amp. Any more suggestions?
Thank you

I could be wrong...It maybe your amplifier passing DC current to the driver. This is bad!!! It will fry your drivers if you continue to use it.

Turn the woofer amp off and disconnect all IC cable. Turn it back on. If the cones pump, it's the amp causing it.

Turn-on and turn-off thumps aren't necessarily bad but depend on severity IMO. How far do the cones move on turn-on/off?
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Could be some type of problem with your amp...something subsonic oscillating going on...or, more likely, feedback.

Like a mic when you get it close to a speaker and you get high pitched feedback, if your speakers are causing feedback by vibrations getting back to your source cd.

If this happens at low very low levels...it is likely electronic...if it only happens at mid to high volumes..it is more likely feedback.