Having trouble diagnosing a noise that occurs during medium effort braking. The noise is absent during light and heavy braking and is always present during moderate braking. It started about 3,000 miles ago and has gotten a little more noticeable recently. It's not a metal to metal sound. It sounds like a mud tire rumble or like I'm on a rumble strip. Tires are Micheline LTX M/S with 30,000 miles and have a lot of tread remaining. This is the second set that I've had and the first never made any noise for the life of the set. I've checked the brake pads and rotors twice. Pads are original, measure over .150" thick and look good as do the rotors. Front wheel bearings were cleaned and packed about 10,000 miles ago and still feel fine. Cannot detect any issues with swing bearing or U-joints. Differential lube is full and has 10,000 miles on it since it was changed. The noise only occurs during braking. I am about ready to service the brakes just to see if that cures the issue. I figure after 119,000 miles on the original pads, it can't hurt. Any ideas?