I've had my truck for a while now its a 04 f150 heritage xl 4x4 with a 4.6l. I noticed that around 40-45 theres a loud whining noise coming from the rear. Its weird because I only hear it at about 40mph then it gets louder until 45 then any thing faster or slower it stops. And also I only hear it while I press the gas.
Any one have an idea of what this could be? thx

 

Sounds like the pinion bearing/bearings are going out.My 97 did the same thing and it was the pinion bearings and one of the carrier bearings.

 

+1 , mine too.

 

thx for the info, how much did that cost you to fix?

 

Well,mine was an open 8.8 differential.Total rebuild,from wheel to wheel,excluding axles,was $800.It included;US Gears,carrier,all bearings and seals,spider gears,and after 500 miles the initial gear break-in lube change.

 

BTW,what part of Florida are you in? This is where I had my work done;
http://www.agearworks.com/

 

thx a lot, i live in Tampa area

 

Well then,Alans Gears is in Clearwater.They will do an excellent gear install job if you take it there!

 

Mine was warranty work. Happened at 7000 miles. 30000 since though and has been fine.