Scrolling Issues

Having a very weird issue with one of my recording projects: When scrolling horizontally in Track View, different tracks scroll at different speeds.  These are all audio tracks, no midi, and I have Clip Contents displayed so I can see the waveforms.  As I scroll, most tracks stay lined up with the ruler but some will suddenly scroll (either left or right) much faster.  So the waveforms do not line up properly under the ruler, ie the waveforms can appear at different time points than where they really are.  It is very noticeable on tracks that contain only occasional audio (such as percussion or bg vocals).  I can set the Now Time to the beginning of a waveform, and as I scroll I'll see the waveform appear to start before the Now Time or after the Now Time, depending on how I scroll.  The discrepancy can be up to about 6 seconds.  What's more, the problem occurs in different tracks in different parts of the song.  BG vocals tracks which are all over the place near the beginning of the song are fine near the end, at this point it's the bass track that won't stay lined up with the ruler.  When I play back the song, some audio parts occur as much as 6 seconds before or after their waveform picture.  (Aurally the song is fine, everything plays in its proper place; it's just the visual representation which is haywire).
 
I've checked through my other songs/projects, and this is only happening on the one project.  For the life of me, I can't figure out what is different about this project, or what I did wrong to cause this.
 
I would like to do some cutting/pasting of vocal parts on this song, which is much more difficult when I can't accurately tell from the waveform where a vocal phrase begins.  More than that, though, it just seems wrong to me that all audio parts don't line up consistently with the ruler.
 
Anyone able to shed any light on this for me?  Greatly appreciated!