A boom at the vents appeared after a larger replacement furnace was installed.

Give the installer the actual pattern

Note whether the sound began on the first day, happens once or repeatedly, and occurs before, during, or after warm airflow begins. A safe recording from outside closed equipment can help if you already have one. Do not run extra cycles to capture another boom.

Ask the installer to check the actual ignition and operating sequence before treating it as a soundproofing problem. If the source is confirmed as sheet-metal movement, ask why the new installation changed that behavior and what correction addresses it.

Ask for setup and sizing evidence

Commissioning means the operating checks made after installation. Request the commissioning record, heating-load basis, and explanation of the new furnace's delivered heating size. A larger label alone is not evidence of a better fit.

Ask whether blower setup, filter compatibility, temperature rise (how much air warms through the furnace), and airflow resistance were checked against the installed model. For example, the Lennox ML296DFVK startup checklist records temperature rise and external static pressure (the resistance against the blower’s airflow). Your model governs its allowed ranges. Lennox example commissioning record.

If a duct or acoustic correction is proposed, get the performer, scope, and price stated separately. An airflow investigation does not mean MGI offers duct work. Ask how the proposed correction will be checked against the noise you reported, with any unresolved ignition concern addressed first.

Your next step is an installer callback centered on the new boom and the original installation checks. Keep the furnace off if ignition is suspected until a qualified professional establishes the operating recommendation.