That wasn't condescending.. Obviously removing it is involved, seeing if anyone is familiar with the issue.
There is no point in trying to diagnose something like that if the transmission has to come out, and be pulled apart anyways...
I've personally never seen a 5R55E or 4R70W Automatic make grinding sounds prior to failure. Slipping, slamming, lurching, surging, etc, but grinding sounds are more common to brake/differential problems.
Does it make this grinding sound after you go from park to drive even if you keep your foot on the brake? If it does, you've confirmed it is almost certianly a transmission noise, and which case there is probably some form of bearing or clutch pack failure occuring internally.
You need to include as many details as possible also in posts like these, that's why I was condesending.
I have no idea what your truck is (sport, or 4 door), what motor it has (4.0 OHC/OHV or 5.0), or what transmission it is...
I am also unsure what circumstance this sound occurs except for when you go from park to drive it briefly makes this sound (As in only while in the truck is in motion, or even while stationary), and you are stating there are no other symptoms.
Has the transmission ever been serviced? every been replaced? how many miles are on the truck? etc etc?