When I accelerate hard in my explorer I hear a thunk from the front end. It does not happen any other time. It seems like it could be the AWD either engaging, disengaging and then re-engaging, but I'm no mechanic.
Any ideas? I thought it might have been the radial bushing arm but they seem ok.

The AWD should be engaged all the time, it's not like the Control Trac system that engages the front as necessary.

Have you inpspected the entire front end for looseness, ball joints, tie rod ends, anti-sway bar links, etc.? How about lugnuts, have you verified they are torqued properly?

Do you have the V8?

-Rod

When I accelerate hard in my explorer I hear a thunk from the front end. It does not happen any other time. It seems like it could be the AWD either engaging, disengaging and then re-engaging, but I'm no mechanic.
Any ideas? I thought it might have been the radial bushing arm but they seem ok.
It is a V8.

Had the same problem with mine. After driving it that way for 3 years, and it getting progressively worse. I replaced the Tranfer Case. $200 at wrecking yard for one with much less mileage on it(47K) Mine had 174K