Replacing the feet certainly looks like the ideal solution. That's a very useful thread, McNach. You have to wonder why Genz didn't fit rubber feet in the first place. If that doesn't do the trick, the cab's the problem.
And yes, BotB, there are plenty of cabs that are reasonably immune to this kind of problem, but the current trend is towards cheap and lightweight - and the lighter you make the cab the more difficult it is to stop it vibrating. Similarly, if you make your cab out of cheap shuttering plywood, as many companies do, they are also going to suffer from this problem.