Shahinian Obelisk vs VandersteenTreo

Well, after a while I finally decided to go for those Quatros and did so.
Got them a week ago and only now got home to update the battery and tune the HP filters and get a dedicated listen.
Unfortunately I discovered that midwoofer on one of the speakers produces distorted sound (especially audible on piano). I did all the fiddling with changing the wires, amps, sources, powering the speaker off, etc, but the middle speaker (right below the tweeter) sounds distorted no matter what I do. The other speaker sounds better.
The seller tells me that all was good with the speakers when he was listening to them last. Also, a week passed since I received them...
So. Has anyone had experience of this sort? What can be wrong with them?

Nuts!
Sorry to hear about your troubles. 
How were they shipped? In their boxes? 
I would call either Johnny R(or PM him), or Mr. V.- he calls back the next day. I believe the Quatro is designed so that you can remove and replace the affected driver with not too much problem- should it come to that.
Bob

One thing to be aware of, Vandersteen matches their drivers within the speaker pair.  One thing to check.  Is that driver tightly screwed into the front baffle?

call RV on Monday
use the Dutch keyboard

Will call JohnnyR, thanks. 
 Wrote  to RV, he thinks this might be the speaker itself. Willing to rebuild it, but oh what a hassle to send it in from Russia and to get it back.  At least 2mo of speakers not working...
Yes, it is tightly screwed.  

A big Q for you Quatro owners: when your power amp is off, but the Q is still powered on, can you hear some slight hum coming out of your midbass speakers? Only audible when you have your ear next to them.
Q#2: did your speakers come originally with some sort of spikes?  If you can, please attach pics.  Mine don't have them, don't know what to look for...
Thanks!