noise from bellhousing after JDM/tranny install

[B F]

Well, I finally finished my JDM swap two days ago, and I've been finishing
up the rest of the car before I move from Dallas to Eugene, OR in 5 days.
Aside from some relatively minor glitches, the install went well, and I did
some modiying while I was in there.  I also installed Courtesy's fifth-gear
pop-out kit.  The mods and maintainance items included a header, new cat,
cat-back, UR 2-piece pulley set, water pump, Outlaw phenolic spacers,
homemade WAI, Prothane motor mounts, fidanza flywheel, and a new Nissan
clutch with throw-out bearing.

Unfortunately, after a few shakedown miles and a trip to a muffler shop to
have the cat-back welded up and installed, the car has developed a nasty
sounding high-speed rattle.  The rattle occurs above about 2500 RPM with the
clutch pedal out.  I'm not sure if it happens with the clutch pedal in, and
unfortunately I'm not near the car right now.  I'm assuming I will need to
remove the tranny to check for loose stuff, but I figured I'd drop a line
here real quick to see if anyone had any suggestions as to what to look for.
  I red-locktighted the flywheel bolts in when I installed it, but not the
pressure plate bolts.  I don't think the flywheel is out of balance because
the rattle developed after some tuning and shakedown driving.  Have any of
you heard of the screws holding the Fidanza friction material coming loose?
Maybe its the throwout bearing?  Any help would be greatly appreciated.