Driving along at 30mph and I have a strange buzzing noise sounds like it comes from the rear of the car. I'veJacked up the car and spun the wheel to see if its the bearing but no noise. I can't see anything that rubbing or any obvious signs that could cause the noise. I replaced the rear discs and pads with mintex 6 months ago. The noise also gets louder at higher speeds. Also the car is a ph1 172 any help would be appreciated.