Hmm........there shouldn't be a squeek there. I was thinking that you might want to check on that rubber part that was on the stock springs and make sure that they were put on your Sprint's before you installed them. You might want to check your upper mounts just to see if they are damaged.
It could be that and I know I had a groan/creak in my front driver's side spring. After a few wheel hops at the track, I guess it finally settled in the right spot and now no more groan/creak. BTW: Wheel hop is the devil.