Logic Pro X cpu spikes

I've got the CPU meter on in Logic as I did in 9. My projects were fine in 9. Now in 10 I'm getting random CPU spikes that produce what I suppose you'd call a crackle. Then they just as mysteriously go away. If I watch the meter I can see a sort of cpu tsunami arriving and then it recedes. I'm on a MBP brand new 16 gigs ram--no reason for this to happen. Any advice? The session in question has a single NI instrument (THe GIant) with a lex 480 reverb plugin. That's it.

Thanks