Replace Caps?

I've been looking for a "bug" in my system...a kind of resonance sound - like something loose and vibrating in the speakers themselves - a "fuzz".  I removed the tweeters which were sent back from the manufacturer as being fine...removed the mids - same story....removed the crossover - same story.  I noticed that the sound gets worse after a couple of minutes of playing....so - out went my 130 lb. amp.  The manufacturer says everything specs out ok, but would recommend changing the caps (2) - fine .....we'll take a listen upon its return.  I've been chasing this thing for over a year.

Changed to other brands of cables, checked for tightness of speaker spikes tightness, banged on everything in the room...had a well known artist create a triptick for the back wall and stuffed the back with fiberglass wool to prevent resonance. Don’t really know what caps they’re replacing but if it solves the problem I’d pay twice. I REALLY don’t want to get the subs out of the cabinets...really heavy.  Yesterday, I got another thought...just ordered Herbies floor protector gizmos.  The speakers are on travertine tile floors  I have the spikes on brass protectors already...I'm trying everything.