-04 Exp. 4WD thump (light acceleration)

[tmzand]

Hi,

When in 4WD hi, mostly during light acceleration or when driving slightly uphill there is a "thump" sound coming from the mid/front. It sounds and feels like riding over a small rock or irregularity in the road. The thump returns every 5 - 10 seconds or so but disappears almost totally on level road and constant speed.

I also have the feeling that, in Auto 4WD, the amount of slip in the rear before the FWD kicks in is longer than before.
Otherwise the 4WD work fine.

I've searched this and other forums and not seen a description of this problem. Any ideas?

(2004 4WD Exp, EB, Air suspension)