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.

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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"
---Marx (Groucho)