Bus errors on 3B2/310

[Paul Siders]

The chem department, U of MN - Duluth, is running a 3B2/310 as the center
of a departmental StarLAN network.  The machine is madonna.d.umn.edu .
The 3B2 is running UNIX V 3.2.  Beginning
two days ago we have been getting some "bus errors":

When booting up:
   /etc/rc2.d/S86win3b  133 Bus Error - core dumped
   /etc/rc3.d/S86win3b  228 Bus Error - core dumped

When sending mail using elm:
   sh: ### Bus error - core dumped  (where ### is a 3-digit number,
                                          different every time)
   then the message is lost, neither sent nor returned nor queued


I reloaded /usr, /etc/rc2.d and /etc/rc3.d from backup tape.

I ran diagnostics (dgn soak) for several hours.  No hardware errors were
reported.

I would appreciate suggestions (please).  
Is this a hardware error?  Is this a software error?
How can I isolate and/or fix it?

e-mail:  psiders at rtchem.d.umn.edu
      or root at madonna.d.umn.edu   (although mail on madonna is suspect,
                                   as described above)