When I initially purchased my 04 STi I swapped out the well worn RE070s for some 960 A/S. Now I just bought some used RE070 to perform better during track events and to not tear up the all season tires. I had them mounted yesterday and they've got a hum over 50mph. It seems to get better as I drive (the tires get warm) but never completely goes away. The noise only started after these tires were put on. I tried doing the tests for a wheel bearing and nothing seems out of the ordinary there (noise remains constant on turns and checked for wheel play).

Is it possible the hum is just the semi-worn RE070 that I'm not used to?
=============
I doubt it. I went through 2 sets of RE070s on my 04 STi and they are a bit noisy when they wear,but it is more of a whine than a hum.
=============