I'll try to make this as short as possible. My truck got a Pink milk shake several years ago when it was my brothers. He flushed it out with gallons and gallons of new fluid, everything seemed to be fine. A couple years later he gave the truck to me. I also did several fill/drains because there were still signs of coolant in the tranny fluid (cloudy look).

About a year later I started hearing this whinning or marbles bouncing around the tranny sound on a cold start up. It did this for about a month before I was able to drop the pan. I found the OEM filter was completely plugged up with a brownish "clay" like material, most likely broken down clutch pack/plate material from the coolant that got in there. I cleaned everything out as good as i could and installed a new filter. The noise was now completely gone.

Everything was fine for a couple months until I started having shifting issues. The issue was my truck wouldn't shift out of 1st gear until the truck warmed up quite a bit (No, this is not the normal won't shift out of 2ND gear until it warms up for emission reasons). It eventually got worse and worse until I swapped in a donor tranny.

Moral of the story, if you hear this noise, make sure you drop your pan, clean it up and install a new filter. I believe I burned up the pump by starving it for that month or so.

Also, bypass the tranny cooler in the radiator or at least replace the radiator every 5-7 years or so, it's cheap insurance.

Hope this helps someone.