N20 timing chain & oil pump drive failure
The 2.0 turbo's timing chain guides wear out early and can fail outright, taking the engine with them; BMW extended coverage to 7 years/70,000 miles, which has lapsed for most cars. A whining or rattling noise from the engine is the warning. Proof of a chain replacement is the single most valuable record on one of these.
Ask for repair records covering this item. If it hasn't been addressed and the car is in or near the mileage window, price the $1,500–$5,000 repair into your offer — or make it the seller's problem.