Master Level Behavior?

I have the master track in the mixer set to show peak+RMS with peak at the top. I'm trying to tame a couple of spots in a song, but having some problems understanding what I see. If I play the song from the beginning, there's a spot about 2 minutes in where the master level (left) shows -2.7. If I then clear the level meters and position the song to start playing about 5 seconds before that point, the highest it ever hits is -3.3. Without actually worrying about whether the absolute numbers are good or bad, why should there be a difference in peak detection depending on where I start playback? (Also, is there anything around that shows which tracks contribute how much to the total levels on the right and left channels of the master?)

Do you have any modulating FX or virtual instruments that could be randomly peaking? That might be another cause. D

Yes D! Didn't even think about this. My thoughts always seem to go from behind, through the chest right into the eye. -Data

Thanks, guys! No, there's no randomization in the processing that I can think of; just audio tracks with EQ, compression, reverb...and the *differences* in the peak readings are fairly predictable. The meter update thing makes a fair amount of sense -- I hadn't even noticed its existence. I don't have much of a CPU load, so I'll try the more-frequent update experiment to see how that works.