I think that may be it because to of legs have nice thick ones but one has a small one that I'm guessing was put on after.Here's one that might be a little left of centre. Check your floor tom feet. Is there plenty of rubber on them?
I had a Catalina maple floor tom that made some strange vibration noises and found the cause of it was feeble rubber stoppers on the bottom of the legs. There wasn't enough insulation between the metal leg and the floor and it caused some horrible noises whenever the floor tom was struck.
It's probably a long shot given the Exports should have nice thick Pearl rubber stoppers, but it won't hurt you to eliminate it anyway.