This is a long shot, but try toggling the 'Vsync' setting under graphics effects. I have absolutely no basis for this other than a hunch, so if it fails I'm sorry.
If anyone does notice oddities like this, by all means start a thread so we can look into it. Since there're unlikely to be any more official patches, like Grim Fandango we're going to have to come up with fixes ourselves (This has been done very successfully for Grim Fandango, though!).
Fortunately Psychonauts is a console game too so at least those versions should always remain as perfect as when they came out. Only thing I can suggest if you don't ultimately find a fix for this and really can't enjoy it with the problem there.