Musty smell and windows fog over

i have a 2018 Tahoe Premier with approx 21K miles, when you get into the
car you notice a musty smells which almost smells like animal feed with
somewhat of a sweet smell with it.. i noticed this past week when driving with
the climate control feature on the windows will start to fog over on the inside.
When you switch it to defrost mode it disappears as it should.

We live in South Dakota where temps can vary.

My concern is that there is an issue with the heater core or a coolant leak.

Can you advise?