Squealing brakes

I had new brakes put on my Audi TT by the dealership last year. My rear brakes have had a high pitch squealing noise when I brake ever since. Sometimes it is worse than others; sometimes it doesn’t happen at all. They have replaced the (new) pads, applied anti-squeak stuff and scrubbed the pads, all to no avail. This sound is so loud and high pitched, that it’s downright embarrasing. What can be done to stop this? Please help.

Sounds like they used the wrong material pads (metallic, semi-metallic, etc). Change to the right kind.