Ok, I've done countless brake jobs before and never have I ran into this problem. But I was trying to do my rear brakes cause I noticed the pads thin. I did what you're supposed to and for some reason the outside pad didn't have enough clearance like the inner pad. The inner pad had more than enough clearance, WTH is going on?! Sadly I don't have pictures to show. Does anyone have a clue?

Before anyone asks, yes I compressed the piston back in.

 

Yes this is a very common problem. Your slide pins are frozen. There is a tsb on this, bring it to the dealer for a free fix.

 

Special service campaign (SSC) 9LB covers this issue. You may want to look this up before you head over to the dealership.