i've been having the exact same problem for the last month now. i have an 05' coupe w/45k miles and had my brakes checked. midas said nothing wrong, brakes still good.
so from my understanding from reading the info on here so far it can be:
-bearings need greasing
-rocks or deposits in brake assembly
-brake assembly needs lube behind the pads
-or the brakes aren't retracting properly....

I think that its the last one in my case because it feels and sounds like the brakes are rubbing slightly still even while driving. my passenger even said something and it seems to come and go. if this is the case what should i do to resolve non-retracting brakes? maybe you can help me lantanaTX, I know you're pretty knowledgeable about brakes and assemblies