ls400 tranny is wining really loud

[underdog51]

I have a 91 Ls400. My transmission makes a really lound wining sound when it is cold. after about 5 minutes of driving it goes away. Or it will sometimes make the noise when i put it in reverse. I dopped the tranny pan and replaced the filter, (i thought it was a clogged filter). But it still does it. the noise if coming from the very back of the transmission. Anybody have an idea of whats going on here. The noise is consistent with RPMS. I can't tell if it is like a bearing noise or if the discs are slipping inside. thanks for any help

Scott