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.

I still cannot think of a clue there is anything wrong the EE MM but the power amp. It is because any amp that would have a problem being driven by any source having a Z=1.5k isn't worth its design...

Ykm - I don't think it's the amp. The person who sold me the EE MM has a dealer who pairs this preamp with the SAME power amp, Belles, that I am using.
Just to update the situation - the pre was sent back and tested. According to the seller/distributor there is nothing wrong with the unit so I am back at square one. I've decided not to go with a minimax and got a refund and will start looking at other options. Just to be extra safe I am sending my speakers back to Tyler Acoustic to have them checked out and will probably do the same with the amp.

Bobby -

I checked the line voltage and it seems okay. I should qualify this statement with the fact that I bought a line voltage meter at Radio Shack. I don't know how accurate these things are but after testing my outlet at different times of the day it is within acceptable range. 120-126V.
When I first put the Minimax preamp into my system there was a very loud hum and some static pops coming through the speakers
Amazing that the pre tested OK.
Re, testing: Rather than the speakers, shouldn't you be sending the amps for a check-up??