My '91 EB 4x4 with automatic trany and 200,000 miles, has started making a very loud "buzz". The buzz occurs only when I'm already in high gear and starts just before the trany begins to auto downshifts during a light acceleration while cruising at 45mph or higher. The buzz stops immediately as soon it downshifts, or if I back off the accelerator. The trany fluid is full and appears very clean. The buzz is a strong vibration which is easily heard and felt throughout the car.
Anyone have any ideas what the problem might be? Loose vacuum line, dirty filter, trany needs flushed out???
Thanks in advance,
Mike