

the /var/log/
folder would be the best place to start.
-
When a random freeze occurs note the time. Try to be as accurate and close to the time it happened as you can, including day, hour, and minute.
A. If possible, do this for multiple instances of this happening -
Check various log files starting with
syslog
and look at the times noted above. Look for any relevant errors being thrown by the system at these times.
I mean, potentially not that quickly if they have to wait days for it to happen. Good low-investment-of-personal-time-and-effort suggestion though.