Screeching Noise in Reverse Gear

[C J R]

Hi,
Along with all my other problems associated with my new RX, I have to ask your opinions on a screeching noise which sometimes occurs when the clutch is under load in reverse.
 
The noise is not gears grinding, but definately like a clutch release bearing type screech.
It does not always happen.
 
The car has an ACT 6 Puck clutch with lightened ACT flywheel.
 
Do you think its a simple replacement of the clutch release bearing ?, if so where could I buy one from ?
Or could it be the pilot bearing ?
 
Your opinions are welcome.
Thanks
Chris