I always just assumed that the “vent fan” over my gas stove actually, you know, vented. After reading your comment I became suspicious of my fairly typical setup and, sure enough, when I turn on the “vent fan”, it’s being blown out of the top of the unit. Wtf.

I never made the connection that the thing is so loud not because of the fan but because the exhaust air is being forced through a relatively narrow area between the front of the unit and the front of the cabinets above it.