Faint click from speakers

Hey Folks - was hoping someone here could help me out. I recently put together a system in a new house that consists of a pair of ProAc D38s driven by Cary 805Cs and a Cary 98p.

Everything sounds great except sometimes I hear very feint clicking or popping sounds from both speakers. The clicks usually start up after the system has been playing for a few hours and fully warmed up. Then the brief clicks start and continue every 4-6s coming from both speakers. They sound like the pop from dust on an analog record but very feint, and they do not get louder when I adjust the volume on the preamp. I've tried shutting off the preamp and sources, but the clicking continues. I've also put the amps into standby mode and that doesn't help either.

It seems like the source of the clicks could be the power from the wall outlets. I have everything connected to a PS Audio quintet, and I don't have any other power regulator/conditioner along the circuit.

Any ideas? Thanks in advance.