I'm getting occasional audio "blinks." These are on playback only; they occur at random and non-repeatedly times. They are on all tracks simultaneously. It is not PC hardware; I have an I7, 16 gigs of ram, and the meters are barely budging. I have eliminated the speakers/headphone amp; at this point I'm thinking it may be the audio interface? MOTU 24/I (predecessor to the current 24 I/0) with PCI card. Any clues? Hints on how to track it down? Thanks!

What version of Windows? 32 or 64-bit? 

The most common problem of this kind, though this may not be the case, is the wireless network / wifi connection - if it's on, turn it off and see if that is the caused ?

This is the tool to check spikes, etc.. 

http://www.thesycon.de/deu/latency_check.shtml

Did you try adjusting the audio preferences, Buffer size etc?

Latest audio interface drivers?