When my 4311Bs are connected to the amp and the amp is on, both woofers are moving when no signal is applied and the volume is down - maybe 10-12 cycles per second. One of the woofers moves so much I would call it flapping - really quite a large excursion.

If I plug the ports then the flapping stops.

If I swap channels it's the same speaker that flaps. I know I need to try them with a different amp, but has anyone come across this kind of thing?

IanG