I've got a 2003 EB 2WD and it does the same thing. I had a wheel hub start going bad but the noise would change if under load and I was able to determine whcih hub was bad...changed both to be safe. I have the rear end clutch shudder which I keep under control with lots of friction modifier, but before I knew what it was I thought for sure it was coming from the front. The whoomp, whoomp noise sounds like one or more tires, but I run Michelins and they have been great tires and the sound does not change when rotated. It makes sense that the noise may be coming from somewhere else in the drivetrain. If you ever figure it out please let the rest of us know. It seems to be more of an annoyance than a serious concern right now.