Weird Version 24.6 Trial Factoring Behavior

[RMAC9.5]

My Athlon XP 2400+ has been doing trial factoring for several months. It has consistently been taking longer to trial factor a number than the estimated completion date displayed by the status command. When I got curious tonight and started watching task manager, I noticed that my CPU appeared to be throttling (i.e. running at 100%, then 0%, then 100%, etc.). However, cpu temperatures were not that high (50 - 54 degrees Celsius) and changing the FSB speed and CPU speed made no difference. For approximately 12 seconds of each minute, Prime95 verson 24.6 would drop to 0% cpu and System Idle Process would jump to 99 or 100%. Not only did this cycle repeat every minute, it occurred at approximately the same time for every minute (from 20 - 25 seconds to 30 -35 seconds). Prime95 version 23.5 does not exhibit this behavior; it runs at 99 - 100% cpu all of the time.
Does anybody have any ideas?