I think it's the brakes... maybe?

I have a 2001 Jeep Cherokee with over 107,000 miles on it. I have an issue that has come up with the front left break (Disc). The problem that occurs is after the breaks are applied and then released occasionally there is a groaning that will come from the area of the driver side front wheel. The sound replicates that of a metal on metal groan much like if you had break pads that were out. this sound will only happen after the breaks have been applied and will stop once the breaks are re applied or after “x” amount of time driving. Accelerating increases the sound but it will stop after a given time period. I changed the pads and rotors about 300 miles ago and they look to be fine, the ball joints are lubed and because I thought it was a sticking caliper I thought that I would replace the caliper bolts and grease them up extra well (needless to say that did not work or I would not be posting). Any ideas about what is going on… Anyone?

My guess is that the caliper is sticking (the cylinder inside, not the outside assembly that you greased). It could also be that one of the metal springs designed to warn you when your pads are getting thin is bent and contacting the caliper.