Boom is a low frequency interior noise of 20-60 Hz. Sometimes the customers complain of a pressure in their ears. Examples of similar noises include a bowling ball rolling down an alley, deep thunder, or a bass drum.

A customer may use the following words to describe boom:

Boom may be accompanied by a perceptible vibration (roughness).

Moan or Groan is a sustained tone at a low frequency of 60-120 Hz, somewhat higher than boom.

Examples of similar noises include a bumble bee or blowing air across the top of a soda bottle. A customer may use the following words to describe moan or drone:

Moan or Groan may be accompanied by a perceptible buzzing vibration. Inspect the following systems:

Howl is a noise at mid-range frequency of 120-300 Hz. This sounds like the wind howling.

Whine is a prolonged, high-pitched sound in the 300-500 Hz range. Whine is usually related to the meshing gears or gear noise. Similar sounds include mosquitoes, turbine engines, and vacuum cleaners.