2003 Explorer transfer case issue.

[uniquesdw]

Here is one that even my local AAMCO guy, who otherwise is fabulous, can't figure out. I have a 2003 Explorer XLT, V8, 4x4. When driving above 45 mph or so and backing off, there is a "thumping" sound that you can even feel in the drivetrain. It is subtle, but it is there and continues "thumping" until you lock in the 4 wheel drive high. It then quits. There has also been an increase in "whine" from the drivetrain over the past few months. This Explorer has just turned 100k miles and the transmission fluid was changed at about 70k. Any thoughts?:exp:

 

[BrooklynBay]

Welcome to this forum! I've moved your thread to the transmission & transfer case section. Check the U joints, and the driveshaft to see if it's slightly bent. I had this type of problem in my 88 one time. The aluminum driveshaft was a little bent, and it put stress on the U joint. In your case, it's possible that it's an internal problem with the transfer case since the problem goes away in 4Hi.