98 e150 4.6l trans whinning
 

I have a 98 e150 4.6l, the trans is whinning starting at 25-30mph and gets louder as i go faster but the whinning goes away when i let of the gas pedal. I changed out the fluid and filter(fuild was burnt up and i found what looked like a big flat metal ring broke up in the pan). It shifts fine so i'm not sure if it needs replacing or something else.
Thanks!