yeah, the center bearing deal, unless the vibration is independent of vehicle speed. I mean, if it happens at 2500-3000 rpm regardless of what gear you're in (the speed you're going) it's prolly not that support bearing. If it always happens at the same vehicle speed, regardless of engine rpm, that's a good candidate for ya. Mine was worst (the center bearing) at pretty low speeds, like 30 or so. Worn U-joints can do that too.