Not sure if this is just sheer coincidence or not. Recently upgraded mac os to maverick and now when my little phatty/sub phatty audio is running through the DAW I am getting a pulse and a click which is in time with the rate LFO of each synth, which as you can imagine is absolutely infuriating. I have tried almost everything from switching between 32/64 bit mode, re-installing the firmware, unplugging everything trying both logic 9 and logic x and no joy. Has anyone had any similar problems? Any advice is very welcome.
Thanks
Fact is, a “real” computer is much more prone to crashing than a “toy” one… 
Mavericks has caused me a little headache too when I installed it. Took two days for my Mac to get back up to speed (literally). But now everything is running smoothly (even a little faster in some case).
Some software/hardware might not be 100% compatible with this new 64 bit OS however. Have you checked on Apple Support or Logic9 support forums ? You might not be alone.
Me, I don’t even have a MIDI interface with my Mac. I record everything OS (Old Style) in Audacity, track by track by hand. Very little MIDI and when I do, I use my trusty old Ensoniq SQ80 as MIDI sequencer.
It could also be coincidence, and a ground loop is the culprit ? Who knows… 