93 Tracker Intermittent growl fm Transfer case area

With Hubs out everything sounds and works great. Turn in the Hubs, and I get an intermittent Growl from under the 4wd shift area.(I assume the Transfer Case). If I shift into 4WD, the growl stops.

NO growl in 2WD or 4WD. Only in 2WD with the Hubs turned in. And also it don't seem to make any difference if warm or cold. Does seem to happen at slower street speeds...20-40 mph.

Thanks for any help.