Is it normal for a furnace to make a popping sound?

Metal ductwork expands slightly as warm air moves through it and contracts as it cools, and that produces the light ticking or popping sounds many furnaces make throughout a heating cycle — completely normal and not a sign of a problem.

A louder bang, especially one clustered right at ignition, is a different thing: it usually means gas is building up slightly before ignition happens, so it ignites all at once with a small bang rather than lighting immediately and smoothly. That's worth a look — it's not usually dangerous in isolation, but it's a sign the ignition system needs adjustment, and it does add wear to the heat exchanger over time if left alone.