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AC Repair
Common Furnace Noises and What They Mean (Boom, Bang, Whistle, Click)
Your furnace is telling you what's wrong. Here's how to translate the sound into the likely cause.
August 22, 2025 4 min read
The sound-to-cause translation guide
Loud BOOM at startup = delayed ignition (gas builds before the burner lights, call immediately). BANGING ductwork = expanding metal (often harmless, sometimes a sign of restricted airflow).
WHISTLING = dirty filter or undersized return. CLICKING that doesn't lead to ignition = failing igniter or flame sensor. SCRAPING metal = blower wheel hitting housing (turn off, bearing failure).