If my fermentation is vigorous enough, the star san in my airlock will start foaming and the air rushing through the foam in the tiny holes on top of the three piece airlock makes a high pitched whistling noise. Really freaked me out the first time I heard that coming from my closet.
Kind of like the evil monkey in Chris's closet (from "Family Guy")
I've stopped using StarSan in my airlocks for this very reason.
To OP, why not get a cheap box fan to make some white noise? I got one to block out the noise of my ANNOYING neighbors (constant yelling and piano playing) and I can't live without it now.