SPDIF Digital Noise

[Giotto]

Using Cubase SX on a G4 933 and having a problem with recurring digital
"snow" and "crackling" popping up after several minutes of use.   I am
using a DBX 386 as a converter to the SPDIF on an RME 9652 with the RME
OSX 1.0 drivers.

I even recently started syncing with BNC word clock using the 386 as a
master and this is still popping up.  The only thing that cures it is a
reboot of SX.  Then after 10-15 minutes, its back.  The noise only 
happens
when I am playing, and not during silence.

What gives?  Any ideas would be killer.  Thanks, Giotto