Thumping noise in tire

I have a '01 Saab 9-3 convertible with 40K on it and relatively new tires. Recently it has started to make a thumping sound, I thought I might need my tires balanced but just took it to my mechanic, who w/o even putting it on the lift, thinks I need new shocks and two new back tires, b/c apparently, if I balanced them and rotated them, they would still make this same noise. I had another saab for years and have never had to replace shocks on any of my cars. I just don't know if this is overkill or not. :(