Push Button Transmission question

[PiscesM21@xxxxxxx]

I have a quick question about a 57 Imperial Push Button Trans.
When I start it up in "N" there is a noise like a sloppy belt but if I put it 
in "R" or "D" the noise quits, and if I leave it in that position 30 seconds 
to a minute before I put it back into "N" it doesn't squeak anymore. The 
trans is engaged and will move. 
Any ideas?
Thanks
Charles in Calif.