If you installed a pilot bushing instead of a bearing this is more than likely your noise. Very few throw out bearings make a whistling noise. With a bushing, the input shaft likes to stick to the bushing causing a "whistling or a screach noise at idle and when just taking off from a stop. GM had this problem for years, and I had several other makes of my own,(Fords and Jeeps)
If a bearing is not avalible, 6 small groves evenly spaced inside the bushing will eliminate the noise. ( hacksaw blade works, been there done that many times) Gm fix at one time.
Good luck
