Popping from transmission

I have an 89 f150 4x4 manual transmission, when in gear (second mainly) and you let off the gas to let it coast, loud pops come from under cab (about where tranny begins) any info if it’s internal or bad tranny

I have never heard “popping” noises coming from a transmission.
I would suggest that you check the transmission mounts, and possibly also the motor mounts.

Will do! I’ll keep updated!