I have the weirdest noise in my 2001 2wd, 2dr Blazer. About 10 feet after moving forward/backward, there is a loud "bang" that sounds like it is coming from the driver front side. I had it to the dealer several times, and they cannot find the problem. It will only do it once once the car is on. It will do it again if you turn it off then restart it. The dealer has removed/checked the front suspension to no avail. Anyone have any thoughts? Thanks.

I'd check if the rubber driveshaft gaiter boot is secure on the inboard side? The noise might be the slack boot lashing around for a revolution or 2 of the road wheel/drive shaft then settling down.
Look for green grease splashes on the drive shaft and Gaiter this indicates the boot has expired (replacement kits are inexpensive) fitting is awkward for the DIYer
If you can push the rubber outwards and see grease or its split /show signs of perishing ? do replace it ASAP
BTW On the Compulsory Annual vehicle roadworthiness Test in the UK (for vehicles over 3 years old) this Item is scrutinised very closely