Mainstage with Presonus Studiolive 16.0.2

So I've recently acquired a Studiolive 16.0.2, which is generally awesome, but I ran across something annoying the other night, which I'm hoping someone can shed some light on.

I had my guitar hooked up to the mixer, which was connected via firewire to the mac, running my normal Mainstage performance rig. All was fine at first, and the sound was great, but after a while, I noticed a crackling static like sound on my guitar channel each time I changed patch. It would be there for a few seconds, then disappear. Then as I continued through my set, the problem got progressively worse, until it remained permanently and turned into a sort of digital 'gargling' sound. Only exiting Mainstage got rid of it.

Incidentally, I tried the dry guitar signal direct through the mixer and it was fine. Also, there was no problem with the playback which was also routed through the Studiolive.

Any ideas?