Heating Fan making squeaking noise when using instrument panel vents and floor vents

Whenever I turn on the heater on my 2016 Hyundai Sonata and use instrument panel vents and floor vents, there is a squeaking noise coming out. The noise sounds like chipmunks or birds.
However, when I use defrost vents (both rear and front) there is no noise. What could be the issue? Are all vents using the same blower motor? Or are there different blowers for defrost and front and floor vents? Thanks!

I don’t know how your hvac system is configured, but most likely either some debris has got sucked into the vents and is hitting the fan blades, or the fan motor’s bearings are dry or faulty. The motor and fan ass’y will probably need to be removed. If that’s not the problem there may be an obstruction in the vents somewhere that’s creating a whistle effect.

There is a chance that this might be still under warranty. Call the dealer service dept., the worst they can say is no.