I wouldn't drop the pan just to change the filter, but if you do plan on checking the solenoids, then, it might not be a bad idea to change it. I replaced my transmission filter when my car had something like 250k miles, and the filter still looked like new.Hinge wiring tutorial:
http://www.lexls.com/tutorials/lighting/bulbout.html
-Blake
I just bought a '91 ls400 2 months, excpet I paid 2500 for mine with 190k miles. I might be wrong but I think that tapping noise is the valves. They probably need to be adjusted. It was more like a ticking rather than a tapping.