Intermittent winding down hum noise when driving

I notice that among all of the alarming sounds my car makes, this one is the most mysterious/less obvious. Every time I drive my car somewhere I hear a winding down kind of continuous hum. It’s hard to describe. a whining noise? I will try to update with a video of the sound soon. The sound appears a couple times in a ten minute drive. Not at any specific speeds. Not when accelerating. And not when braking. Not at idle. I tried to summon the sound doing all or those but it just wouldn’t appear. Though it does happen while I’m doing any of those things, it randomly appears with no trigger and goes away after about 15 seconds. Seems like it’s coming from the passenger side of the car because when I drive it doesn’t feel very close to me? Anyway not a lot of detail but hopefully someone can give me a clue as to at least what system or part could be failing.