This plate is from the bottom of the caliper. Mine has a broken tab! And causes it to creak and squeal. Anybody?

GT or ST? Your profile says you have an ST. Are you referring to the backing plate?

I did a rear disc brake swap from a GT. One of the pad support plates (in the shape of a U - I'll take a picture if absolutely needed) is missing a small tab. The missing tab causes the plate to vibrate which then causes an obnoxious noise. I just added some caliper grease to it as a temporary fix, but every time it rains I have to reapply. Somebody help me!

The pad supports can be purchased at any autoparts store; they come with any set of pads, but can often be found in a pack of brake hardware.