You could conceivably have leaves or other foreign matter down next to the blower motor. Stuff can get in there through the fresh air intake cowling, located on the outside of the car just below the bottom edge of the windshield behind the rear edge of the hood, where the wipers are. On some cars things like paper clips and pencils, etc., can fall down through the defroster vents on the dash and get in there too. I've had both things happen. Or you could have a bad blower motor or fan or bearing. There are lots of YouTube videos on this stuff. I would want to get it fixed before it causes the blower motor to become stuck and burn up.
It happened to me and the noise was unbearable so I ran to the dealer. The tech came out to the car, removed the glove box, took out the cabin filter, turned on the fan and a whole bunch of Locust leaves blow out. He cleaned up the leaves, put everything back together and sent me on my way in silence. He also said that one time he found a live squirrel in there.
Ours ('17) had an issue with the fan squealing intermittently so I video'd it and made an appointment at the dealer who listened and made arrangements for a fan replacement which solved our problem.
My suspicion regardless of make is if you leave a window or sunroof open, and have a mouse or chipmunk problem, that they enter the heating system through the intake of recirculation part of the HVAC system.
The only true solution is a pest/bait control program
Of course, all these tips assume that you bought the car new. If you bought it used, there are some other possibilities. If it was previously used to smuggle dope, I'd want to get that issue addressed ASAP. Or it could be that either you are or the previous owner was under government or alien surveillance, in which case I cannot advise you further and you are on your own. :kaboom