I agree with paintmann. If the wheels were older, corrosion can be another possibility. If you use the same wheels and tires year round, I suggest having a tire shop dismount the tires and cleaning the tire beads and area of the wheels where the tire beads seat to get all of the salt and other corrosive contaminants out of there after every winter season if you don't do this already. Same thing if you have a dedicated set of snow tires for the winter, but use the same wheels. Other than that, I have also seen cracked wheels from hitting bad potholes and bent wheels where just the rim of the wheel was slightly bent, just enough, causing the bead area of the tire to not sit flush with the wheel.
Eibach Pro Kit, Dual Flowmaster 40 Series Axle Backs, 18" Milanni ZS-1s, 245/45R18 Falken ZE-950 Tires, Smoked Front Marker Lenses, Limo Tint, Pioneer Double Din, Alpine & Kenwood Speakers, 12" Kicker CVRs, Alpine Amps, AM Paint Matched Side View Mirror Caps, LED bulb conversions everywhere
, more to come... need to sell OE wheels/tires and suspension first.