This sounds like at least one of your tires has a tread separation problem. Run your hand over the tread and sidewalls and check for bulges.
Usually they bulge, then the tread comes off. This is not safe.
Semibodacious Transmogrifications a Specialty
1990 300D 2.5 Turbo sedan 171K (Rudolf)
1985 300D Turbo TD Wagon 219K (Remuda)
"Time flies like and arrow, yet fruit flies like a banana"