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.

DC would push the cones one way or the other. The only way DC could cause a cone to move back and forth would be the DC alternating between positive and negative like switching the leads on a battery.
For example, if you take a "D" cell and connect the positive to the positive on the speaker and the negative to the negative, the cone will jump out and stay. If you reverse the negative and positive, the cone would go the other way and stay.
As a matter of fact, DC does not have frequency. It doesn't alternate like a sign wave(AC.) It travels in one direction. An amplifier produces an AC signal to the speakers. For DC to cause your problem, how did it get through the amp. I would also think that you would be hard pressed to get enough DC through your amp for it to do this. If the amp has a DC servo, it would block the DC to the amplifier input stages. If it uses an input cap, it would block DC.
I think you have a very, very low frequency modulation problem(modulating AC)coming from one of the preamp amplification stages. I would contact the manufacturer.
Just to update . . . I removed the CD player from the loop and this had no effect. It's looking like it's the preamp.

Bigtee - thanks for the post. I don't know enough about electronics to have an idea about DC vs. AC but I will definitely bring it up when I speak with the seller.

Thanks to all who posted.
I'm pretty sure it's the preamp and the person who sold it to me seems to agree. This one's going back and a replacement is on the way. Thanks for all the suggestions and insight.
I've no idea what's high-freequency DC(probably something brand-new in EE) but BAT has tendency to drain some DC at the output.
Probably the same story with your pre which isn't neccessary because of bad tube...
DC ??? absolutely not. High frequency DC...what is that ??? Please tell us how high frequency it is, DC with frequency and still called DC ???

What you are experiencing is subfrequency motorboating, or, in other words, an unstable power amp that is probably only marginally stable with the speakers you are using. You might have been using a pre with a higher output impedance and just got away with it. However, with the low
Z of the EE MM, that puppy becomes likely unstable.

Anyway, w/o knowing what you are using, it's just my logical conclusion, not gospel...