FWIW, here is the troubleshooting info from my '86-'93 Haynes manual for a "noisy" TC:
1. Lack of oil in TC.
2. Noise in 4H and 4L, but not in 2H indicates cause is in the front differential or front axle.
3. Noise in 2H, 4H, and 4L indicates cause is in rear differential or rear axle.
4. Noise in 2H and 4H but not in 4L, or in 4L only, indicates internal wear or damage in TC.
I hope this helps and I hope it's something simple.