Most likely, a cracked rim like everyone else said. They usually are perpendicular to the edge of the wheel, travel through the lip and are on the inner lip of the wheel, making it very difficult to see without taking the wheel off the car.
If it is cracked, it can be repaired. I had one with two cracks in it fixed about 7 years ago and it's still good
Dinan CAI &Throttle body, ESS Tuning TS2, Bimmerbrakes gen3 headers, UUC SSK & DSSR. Achilles oil pump, VAC oil pan baffle
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