I have a stereo set of ACI Force subwoofers that have given me excellent service for about twelve years now. Recently, however, I've begun to hear a random "thump" from one or both of them periodically. The power switches are not easily accessible, so they've always been left on, and this happens even when the rest of the system is completely shut down, i.e. nothing is powered on but the subs. This is not associated with turn-on, and there appears to be no pattern to it.
Mike Dzurko made a great product, and I obviously can't complain about the service I've gotten from these, but ACI has been out of business for some years now. Any suggestions on what might be causing this and how/where to get it fixed would be welcome.