linux clock drift

I have a problem with clock drift on an opteron machine running suse 9.2. I think I've narrowed the problem down to the kernel clock. I stopped NTP so that isn't confusing the issue. I manually set the system clock and the hardware clock to match another NTP-synchronized clock that is working properly and left it for an hour. The hardware clock is still showing the correct time, but the system clock has gained 52 minutes in an hour. Can anybody suggest where to start looking for the source of the problem? Thanks, Dave