Going through tires?

[Dr. C]

New here and I have a handful of questions about my '04 X3. I'll split them up, one per post. Bought my X3 CPO from a dealer approx 18 months ago with 24,000 mi. When test driving I heard a lot of tire noise and the dealer determined that the tires were cupped. I asked if this was up to CPO standards and the dealer put 4 new tires on before I bought. 20,000 miles later the noise is back and dealer service dept says tires are cupped again. But they offered no remedy besides selling me 4 new tires. I'm guessing this is an alignment problem, though the car tracks in a straight line. I'm pretty religious about tire pressure--keep a chart of my vehicles' recommended tire pressure on the garage wall and have an accurate gauge. Should I expect my X3 to go through tires like this? Anybody else have a similar experience? Other than escalating to service manager or higher at the dealer, do I have any recourse under CPO program? Thanks for any thoughts.