clunking sound from left front end

I have a 97 with 198000 miles. Driving on the highway yesterday and got a clunking/thwacking sound from left front end. Though it was either a flat (because of the sound) or something stuck and rotating with the tire. Checked, nothing there, not the brakes, nothing loose. Kept happening first at around 70 mph, would stop as soon as brake was applied and speed dropped but eventually it kept happening as slower speeds and had to make it home going about 40. I'm thinking maybe the universal joint? Any help is appreciated.:banghead: