Capacitor problem or static discharge?

Hi to all!! I've had my Unity Audio Signature 1 speakers since 1993 (purchased new then). I hear a loud "crack!!" through both channels occasionally, usually brought on at loud but not insane volume, and usually on heavy transients (drums or bass). Would any of you know if this is due to a speaker caspacitor problem (worn caps), or is due to static discharge of some sort? My speaker cables are up off the carpet. Thanking you all in advance for your ideas. Might be new speaker time.--Mrmitch
Are your speaker woofer cones "poly" material? If so, they are doing what all poly cones do when driven hard they produce a 'snap' or 'crack' sound. This is normal for a poly (plastic) cone.
One of the drawbacks of a poly cone material.
If your woofer cones are some non-plastic material, I do not know what is wrong.
It is possible that the voice coil of your woofer may have shifted a little and is touching the center magnet pole. With the amp off, try pushing the woofer cone with even pressure and see if you feel it is touching something.

It is also possible that the wire inside the speaker may have shifted and is touching the woofer cone. In this case, you will need to take the woofer off and look inside.

It is also possible that after years of service, the suspension of the woofer get lose and the voice coil hits the bottom of the magnet when playing music with heavy transients. You might want to look at how the woofer moves when music is playing.

Another possibility is that your speakers are fine but there is something wrong with your amp.

Good luck.