Normal air noise, and the sounds that are new
Moving several hundred cubic feet of air a minute through a metal box is never silent, and a hood that is louder on its top speed than on its bottom one is doing what it should. A noisy range hood is worth chasing only when the character of the sound has changed. Air noise is a smooth rush that rises and falls with the speed setting; mechanical noise has a pattern in it, a tick, a scrape, a pulse or a pitch that does not belong.
Before touching anything, run each speed for half a minute with the burners off and listen from directly below and then from across the room. Write down which speeds make the sound, whether it starts at once or after a few seconds, and whether it changes when you press lightly on the edge of a filter with a wooden spoon.
Rattles and buzzes from loose parts
The simplest noises come from parts that are meant to sit still. Zephyr's troubleshooting table for one of its wall hoods gives a loose metal filter as the whole explanation for a vibrating filter, and a hood that is not secured in place as one reason the entire unit vibrates.
- Sound stops when you press a filter: reseat or replace that filter.
- Sound stops with a hand on the chimney cover: book a refit.
- Whole hood shakes on high: book a visit; the mounting may have loosened.
Filters, light covers and trim
Reseat each filter so its latch clicks and its edges sit flat in the frame. A filter that was bent in the dishwasher, or put back upside down, can buzz against the frame at one particular speed. Light lenses and the trim strip along the front edge can do the same thing when a clip has let go.
The chimney cover sections
On a wall or island hood the decorative cover is two telescoping pieces, and a buzz that seems to come from the ceiling is often the upper piece touching the lower one or the wall. Listen with a hand flat on the outside of the cover. If the sound stops under your hand, the cover needs refitting, which is ladder work with the hood's weight above you, so book it rather than loosening screws overhead.
Source: Zephyr — Firenze ZFI-M90S use, care and installation guide — A vibrating unit: motor not secure, damaged blower wheel (replace the blower), hood not secured in place; a vibrating metal filter means the filter is loose
A damper that chatters or slams
The backdraft flap in the duct collar should open once and stay open while the air flows. On a low speed, or when wind gusts against the outside cap, it can flutter against its seat and make a fast ticking or tapping. A flap that slams shut every time the hood turns off, and flaps again on a windy day with the hood off, is telling you about the damper and the cap, not the motor.
That sound is annoying rather than harmful, but it often comes with a cold draft into the kitchen, and the cure is on the damper or the cap. Both are reached through the chimney cover, the cabinet above or the outside wall, so it is a damper and duct visit.
The blower wheel: rubbing, wobbling and debris
A scraping or rhythmic rubbing that starts as the fan spins up, and gets faster as the speed rises, usually means the squirrel-cage wheel or impeller is touching its housing. A wheel that has slipped on its shaft, a housing knocked out of shape during installation, or a clump of grease that has broken loose and lodged in the blades will all do it.
Zephyr lists a damaged blower wheel as a cause of a vibrating hood and gives the fix as a new blower. Wheels also go out of balance when grease builds up unevenly on the blades; the hood then hums with a pulse, like a washing machine on a lopsided spin. Cleaning or replacing the wheel means opening the housing, which is a visit.
Remote and in-line blowers
If your hood has an in-line blower in the attic or a remote one on the roof or outside wall, a rumble may come through the ceiling or the duct rather than the hood. That layout is quieter in the kitchen by design, so a new noise there is worth reporting with a note that the sound seems to come from above, not from the hood itself.
Source: Zephyr — Firenze ZFI-M90S use, care and installation guide — A vibrating unit: motor not secure, damaged blower wheel (replace the blower), hood not secured in place; a vibrating metal filter means the filter is loose
Hums, squeals and grinding from the motor
Motor sounds divide cleanly. A steady hum with the fan barely turning or not turning at all points to a starting capacitor or a seized motor; switch it off rather than leaving it to hum, because a stalled motor heats quickly. A high squeal that settles after warm-up, or a dry grinding that gets worse over weeks, is the bearings.
Broan's manuals say its hood motors are permanently lubricated and never need oiling, and that a motor with excessive or unusual bearing noise should be replaced with the exact service motor, along with the fan blade. The same manuals warn that drywall spray and construction dust damage bearings and unbalance the blade, which is why a hood that was left running during a remodel often turns noisy within a year.
- Hum, no spin: turn it off at the switch and book.
- Squeal or grind that is getting worse: book before it seizes.
- Clicking at start-up that then stops: note it; often a relay on the control board.
Source: Broan-NuTone — BCSD1 range hood installation, use and care manual — The motor is permanently lubricated and never needs oiling; excessive or unusual bearing noise means replacing the motor with the exact service motor and the fan blade; drywall spray and construction dust cause bearing damage and an unbalanced fan blade
