Today my 2005 Chevy Aveo LT started a shimmy in the steering wheel at about 50 mph. A definite, strong shimmy. I pulled over and inspected all 4 tires and wheels, and gave each one a good shake. Tires are all great. No loose lug nuts. No uneven tread wear. When I pulled back out onto the roadway the shimmy was gone and all was well. 15 minutes later the shimmy started to gradually come back. I'd appreciate any and all suggestions for what I should be looking for when I jack it up. Thanks to all for your help in the past.