Hello, new to this forum. I am a first timer bmw owner and I have 1999 528i auto. The past 3 weeks a problem has developed in my back end. A loose rattle/knocking/pinging type of noise is coming from my back wheels. The noise is faint enough that with the radio on I can not hear it. I can get the noise to stop by stepping on the brakes. I know it is not the brake system because I have had that checked twice. Any advice would be awesome. Thanks to all.