In either case, how many miles on those components? Might be some kind of drivetrain slop from a bad mount somewhere. That can cause strange clunks when going off/on throttle from the whole motor/trans/diff moving around when it should be tightly mounted. BDE OE-Style engine mounts and OEM trans mount would probably be the first things I would try. You'll also want to check your Driveshaft's Center Support Bearing.