Random fits of low fps

[Darkslave]

A little odd problem I'm having here...

Every now and then FFR seems to get stuck in some sord of low-fps mode, where it looks like FFR is running at around 5-10fps, a little comparable to putting stops on every arrow in a 16th stream in SM.
This will last anywhere from around 5 seconds to 30 seconds, then suddenly pop back to normal, just to do the same some time after.

Switching browser between Firefox/IE/Chrome helps nothing, neither does playing outside of browser or turning priority to high/realtime, heck, cpu usage doesn't even spike.

I've had this happen on 3 systems so far, this one, a 1.8ghz singlecore/geforce6150LE graphics card, a 3ghz dualcore/geforce9800gtx setup, and a 2.4ghz singlecore/geforce4 computer, so specs don't seem to have much to do with it.
Also this has happened on both an XP and a windows 7 system.
Some additional info, restarting a song sometimes helps, and all of these systems run the game just fine outside of these low fps moments. Also, timing does not suffer, the game responses as if it's running at the normal fps.
Edit: also happens both with and without hardware accel.

Any idea anyone