Please help transmission problem 87 accord

when i first start the car, a grinding shrieking noise is heard at the transmission when in park or neutral. when you put it in gear the noise goes away. put it back in park or nertral the noise start again. when you rev it up to about 2000 rpm the noise goes away. when the car warms up completely the noise goes away. after it sit for a while and restart the car the noise is there again. it always go away while driving.

Thanks in advance.