Hi there, I have a 2008 corolla ascent, that has been doing this since it was 2 years old. Sometimes it is so loud that when coming to a stop at lights etc, others outside the car in their cars or pedestrians can clearly hear it and look up at me. I was under extended warranty with Newcastle Toyota who when it was taken in for service every time for 6 years, most of the time claimed they couldn't hear any noise or didn't know what I was talking about.
(standard practice for them,about everything,ended up with Dept of Fair Trading involved)
Once they were involved, the issue was resolved with note "applied grease to calliper slides".
It worked for a while, comes back every year or 2, needs to be redone, have noted that apparently ALOT of grease is needed to stop it completely, sometimes the tech has done it with i assume general application, result being only dulling sound not stopping completely. Hope that helps