Are my speakers supposed to do this?

Hi all. Thanks for reading this thread. I just put a new preamp (Eastern Electric Minimax) into my system and am noticing some weirdness in my speakers. When everything is on but no music is playing I noticed that both the left and right drivers of my monitors (Tyler Acoustic taylos) are moving forward and backwards very slowly but at a very steady rhythm. Takes about a second for them to move forward and then another second to move back. They repeat this cycle until I turn the amp off. This doesn't seem normal to me. I never noticed this with my previous pre. When I play music through the system it seems okay, no obvious distortion although I do notice my drivers moving (from my listening position 7 feet away) in a similar way - slow in and out although it doesn't seem as cyclical.

When I first put the Minimax preamp into my system there was a very loud hum and some static pops coming through the speakers. I lifted the ground on the pre with a cheater plug and the hum & static went away.

Did I damage my speakers? I want to try and trouble shoot but am afraid that damage already may have been done and I don't want to make it worse.

Thanks.