When you had the pads replaced (I presume w/ OEM pads since you say a lexus dealership did the work), did they also replace the anti-squeal shims and put the special grease on them? The factory manual says the anti-squeal shims should be replaced when the pads are replaced, but they normally do not come w/ the pads. I had my front pads replaced 1K mi ago. I'm not sure if they replaced the squeal shims (I didn't have the factory manual then), but they don't squeal at all.
What do you mean by special grease?