Bad disk is obviously another possible issue (saw that on a pi
sdcard), but I'd definitely be testing that RAM. Really if you suspect
bad RAM it is worth your trouble to just shut down ASAP and test that,
because every minute with bad RAM is potentially corrupted files on
your hard drive, and rework even if you have a good backup.
Another possible issue is bad -march settings. That usually is an
issue if you change your CPU and boot off of an existing hard drive.
If you're going to upgrade your CPU you should rebuild all of @system
(at least) with -march set to something very minimal. Don't assume
that a newer CPU does everything an existing one does - they sometimes
do drop instructions. You can set -mcpu to whatever you want, as a
bad -mcpu will only cause minor performance issues.