Could you be describing the "Mercedes moan"? If so, it's most likely just the brakes talking, nothing wrong, it has to do with the composite of the brake pad material and "harmonics" of the rotor. Hmmmmmmmm.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.