Portage – September 25, 2026 -- Loud banging, screeching, or rattling from a furnace during winter often signals a mechanical or airflow problem rather than a harmless quirk, according to Bob Marquardt of Johnson Mechanical LLC in Portage, Wisconsin.

Banging sounds may point to delayed ignition

A loud bang at the start of a heating cycle can occur when gas builds up before burners ignite properly. Repeated delayed ignition adds stress to furnace components and can eventually damage the heat exchanger.