That's ugly!
White noise is generally, bad ram, incompatible / out of date plug-ins or hard drive that is failing. But these issues are sometimes hard to track down, just be patient and thorough and eliminate all possible variables.
Have you ran an
Apple Hardware test?
I would get
MemTest and verify your RAM is all passing.
Pull all plug-ins out to a temporary location and see if noise still happens
Mac HD /Library / App Support / Plug-ins (empty this folder out or move it and relaunch PT)
Follow the optimizations
here
Repair disk permissions, airport and bluetooth off, Firewire cable direct to back 1394 port on mac pro (not connected to the cinema display if any!)
Remove log-in items, startup items and disconnect all other peripherals connected to the machine.
If still getting noise, try
Zapping PRAM,
Reset SMC and new 1394 cable.
Good Luck.