I've got a '93 100S and when you apply the breaks while in backing up (not just reverse, coasting in N as well) it will emit a VERY loud groan. Seemingly from the back wheels only but I can't be too sure. No pad wear indicator, no groan when using breaks normally going forwards.

Light or hard breaking, it's always there. Any ideas so I can have something to go on when I take her to the shop?

Thanks!

For what its worth, mine have been doing it since the beginning of time and the brakes are fine. Dealer years ago said it was just the pads shifting slightly - but it did and still does only made noise when I was braking.

Do you use your parking brake? I had that problem before, because my driveway is on an incline, and I use the parking brake (force of habit). So now instead of pulling hard on the handle to set the brake, I just pull it two or three clicks and the groaning stopped. But I still get the groaning sometimes if it had rained overnight or something.