I think I'd take it to a busy Chevy dealer as those mechanics have seen more Ventures than any private mechanic. Noises like that can be very hard to find and are often model-specific quirks that a dealer might well be aware off. I had a front end banging noise on a 99 that drove me crazy and it turned out to be a loose roof rack crossmember nut-- yes roof rack! Because of the unibody design, roof noises on Ventures are often transmitted down through the hollow windshield pillars and come out the front end just like a speaker. It was bizarre -- I tightened the nut and the noise stopped. It's a longshot, but since your mechanic apparently was very thorough with the suspension, you might also look at your front hood hinges (check for play) and locking mechanism. Try spraying some white lithium grease on both. Good luck and let us know how it turns out.