[xlr8or]

B.SMITH,
I was going to suggest that very thing.
I had the problem with an older Z-28 and just couldn't get rid of it by balancing and alignment. I did the balance and alignment myself several times trying to find the problem sometimes it improved other times it was a little worse.. Someone suggested balancing the them while on the car and that worked great by balancing the entire rotating assembly.
Turned out when I replaced the worn rotors a year later I never had the problem again.

Scott