protools, logic pro and sibelius not getting on

I've tried searching for this problem but don't even know what to call it as I don't know what it is. It must be a common one. When logic pro AND protools are open (or sibelius and pro tools) the active track in logic starts pulsating a very low note on the synth. In sibelius it starts writing music (same low note) and you can't stop it! When you quit protools the problem goes away - so these programs are getting a signal from PT - PLEASE tell me there's a way to turn it off? I would really like to have all these apps running at the same time. Going quietly insane. Cheers

Hey Chris, thanks for your reply. Versions are: PT 7.4 Logic pro 8 Sibelius 5 But it has been doing it for years with different versions - it's only lately that I've been losing the plot over it! They're not synced at all. No clocking, no audio routing and no midi interface (although my command8 has ports but I don't use them) you mention an IAC bus eh? Well I'll see if I can find one of those when I'm back at work and I'll try to turn it off. Cheers for the help

try unclicking the "rec" on the active track in Logic. if it stops pulsating then it is cuz PT is somehow sending midi to the track.