I am quite sensitive to unpleasant sounding vacuums. Especially high pitched vacuums are unbearable for me.
Some examples are older Dysons with multi cyclone design. DC 07 is worst I can think of.
Tone of the sound is most important. For example my Kirby Gsix is loud, but it is quite neutral for my ears.
Lux Royal D790 is extremely smooth/quiet sounding and Black&Decker AirSwivel is loud
high pitched screamer.
