Take the speakers off the stands and put them directly on the desk, with the isolators under them and see if the rattle goes away. You need to figure out where the rattle is coming from.
Can you determine if the rattle is actually a damaged/blown woofer in the speaker(s)? It seems odd that with that isolation it would rattle, but if it's running a full range signal, it's certainly possible. A proper crossover should fix that.