Auto trans noisy X300 XJR6

Pulled off the motorway yesterday afternoon and stopped at the roundabout at the end of the slip road. When I pulled away there was a very loud whirring noise which changed tone as it changed into second gear. The sound ceased when it changed into third/fourth/top.
Checked fluid and appeared more yellow than red on the bottom of the dipstick. drove a few more miles trying to find a garage that stocked Dexron lll. After trying 3 garages I opted to phone the recovery company and got recovered home.
Bought some oil this morning and topped it up and went for a run. First of all the noise was there, then it wasn’t, then it was noisy in higher gears as well, sometimes its quieter and sometimes it’s louder. and sometimes no noise at all.
I may have overfilled it as I found it difficult to get a definite reading on the dipstick.
I’m going to order a new filter kit and drain the box and refill with fresh fluid asap but would like some opinions if anybody has any. TIA, Rod