I have a 99 GC with the 4.7 I bought a week ago. If I am applying the brakes pretty hard lets say going from 40mph and I have to stop at a light I get a strange sound. It sounds like something is sliding. The sound is coming from the floor console or behind the dash in front of the floor console. At first I thought it was the brake booster diaphragm but the sound is not coming from the right place. The best way to describe it a small rock or penny sliding across a textured surface. It does not make that sound when accelerating and it does not make that sound with light pressure on the brake pedal. It also does not make that sound when going slow and applying full pressure. It does not make that sound when doing a panic stop. I would say it only happens with moderate pressure on the brake pedal. Any idea? I have not pulled the console apart yet due to other things Im fixing on the Jeep.

 

Check your pads.. some pads have a 'squeaker' on them to notify you of wear.. Also, take a look at your brake fluid reservoir. If your fluid level is much below the max mark, this could indicate pad wear as well. Don't just add fluid to top it off. If you do, when you replace the pads you'll have excess fluid in there.
Since this jeep is new to you, you might want to give it a thorough look over. Make sure brakes are all good Check all fluids, belt, hoses etc..

 

I had a mechanic check it out. He said the brakes are good. It does not sound like it is coming from outside the car and its not squeaking. It sounds like it is right inside the floor console. Its intermittent.

 

Pull the console and see if there is a marble or something that may have fell inside and is rolling back and forth.