Reversing Noise

I had so much luck with my last question that I posted here, I’m going to ask another.
I have a 1995 Lexus ES300 with 130,000 miles on it. When I reverse, I get a low-pitch growling and as as soon as I apply the brakes by a high-pitch, ungodly screech. This noise is definitely coming from the rear wheel areas. I’m not sure which tire is the culprit (I hear both sides from while listening from both the inside and outside). It happens frequently but is particularly bad on rainy, snowy, misty, or high humidity days. Two years ago I replaced the pads and rotors. At this point, the pads look to have about 40% life on them yet. This problem started happening about a year ago.

My initial thoughts were that it was just rusting because of the frequency on high moisture days. But both noises are way too loud for that.
My second speculation was that the emergency brake was catching, but after examining it I think not. I’ve taken the entire assembly (brakes, rotors calipers, and emergency brake) at each tire apart and looked for any obvious issues that look incorrect. No luck. I’ve also applied brake quiet with similar results. Now my thoughts are that the low pitch is the rotors being warped. But that doesn’t explain the screech and why it only occurs in reverse.

Thanks in advance.

It doesn’t take much for brakes to get really loud. You’re talking about the rear and saying that you replaced pads and rotors a couple of years ago, so I’m assuming that you have disk brakes all around. The first question is whether or not your estimate of pad remaining is going by the outside pad only. If your caliper slides are sticky you could be showing good pad on one side and no pad on the other. You’d have to pull the wheel and inspect both the inboard and outboard side.

Other than that, in order to stay quiet brakes require various means of damping vibration. This often includes hardware kits and some well placed dabs of brake grease. This is about the screech. Your description of the growl is vague, but with dampness brakes often make what sounds like a grinding/growling for the first few applications - and it is surface rust being ground off. That surface rust can easily produce more screech (vibration).