help tranny clicking noise when in drive

I have an 88 gmc 4wd my 700 r tranny is making a clicking noise when I put into drive and stops clicking when I put into park or neutral any ideas
what might be causing the noise fluid is full1

Are you sure that the noise is coming from the tranny. Sounds like you may have a bad u - joint. It may start as a squeak then become a click. You may also notice some vibration as well. I would check your u - joints before jumping to the tranny. Just an idea....
:ylsuper: CheckEngine

possibly a cracked flywheel?