I've just had this. Seized caliper warped the disc, go for a drive, somewhere 70mph and when you get back feel the temp of the calipers. If ones hot compared to the other then it will be that one.
Have you had your tyre balance re checked? I wrecked a set of front discs on the ///MR, due to poorly balanced tyres. They where only a tiny bit unbalanced. I replaced the discs & pads, convinced they were the issue. Then over a few weeks the problem started to return. So I had the balance re-checked and re-balanced, until they were more or less perfect according to the guy who did them. The problem then diminished over a few weeks as the brakes cleaned themselves up. then vanished completely. I still have that set of disks fitted.
I power washed the z before hibernation last year and didn't run the car down the road to dry the discs off . Woke her up a few months later and calipers where sticking . Ended up with warped discs . Cheap enough fix though