Torque convertor cavitation?

[myblue67]

 Been trying to ID a cavitation type sound for several weeks, actually going back to last fall. Sounds like coming from torque converter, but only for a few seconds on start-up. No operational problems and level appears to be good. I do have a small leak at the radiator connection (maybe a drop or two over night), but again I checked level and was not even close to the "add pt" mark. Thoughts, experience?  PG transmission in an L48.