i recently got a new transmission put in my 05 f150. I took it out the other day and had to put it in 4wd. (this was the first time it was in 4wd since the new tranny). well i get it back on the road, take it out of 4wd, and when i hit the gas there is a ringing/siren kind of noise coming from the rear end. When i let off the gas its fine. SO i took it back to the the tranny shop and they called back in a few days saying they were dumbfounded. said they had it torn down twice, electronic ears on it blah blah cant figure it out. Does ANYONE have ANY ideas???? someone told me it could possibly be my ring and pinion? im just as baffled as the guys at the tranny shop....

 

Well if it is coming from the rear of the truck, that is a very good possibility.

 

Could definitely be ring and pinion... I've had mine replaced 2x on my '06 KR 4x4 and it is already whining again. I notice it mostly between 45-52mph. I've got 45K miles on it now. Replaced it the 1st time around 20k, then again at 41k, and now it's whining again!