Thanks, rharv. PGMusic support suggested the re-install of PT as a solution about a year ago. In fact I have to delete the PT folder after the uninstall before reinstalling or the problem remains. I only use two non PG plugins but they are both freeware so I'm pretty sure one of them is the cause, but I'm not wanting to give them up. When it gets bad the audio will change pitch in random places and even move randomly in the stereo field. When I reinstall, all is good for a few days.

It's good to know that I can reinstall RealBand on it's own. I'll keep that in mind.