I can never remember where I keep my receipts and warranty stuff anyway. So I generally don't count on em. And I weigh buying stuff on the assumption of no warranty even if there is one...
So in the same situation, I'd probably just be kicking myself for not doing something about the weird noise earlier on. I always take stuff apart anyway(and void warranties) to do modifications, so I probably could figured out the problem and fixed it early on.
So to answer the question of what I'd do:
I'd say 'whoops', then shrug and head down to the local Bike Co-op; spend 150$ putting together a bike from used parts. Happily ride off knowing that my new bike is custom to my taste, well put together, and cheaper than that old lemon from the shop... I'd be so happy with my new wheels I'd totally forget about the mess with that other bike; time to ride.