Musty Smell coming through vents

[Bramski]

For the past week, I've noticed a musty smell in the house. Put my nose to one of the vents and could smell it coming through with the blower running. First thought was possible mold in the ducts. I looked inside the supply duct coming right out of the furnace and didn't see anything our of the ordinary. Looked at the A coil and drip pan, again nothing unusual. What could it be. (Not an HVAC tech)

[Admin]

Do you have a bypass humidifier or HRV installed?

[Bramski]

Do you have a bypass humidifier or HRV installed?

Yes there is a bypass humidifier installed. I just turned it off today.

[Admin]

Often times a humidifier pad can lead to the smell you're describing.  It should be pretty noticeable if you smell it or you can just remove it completely and see if the smell goes away.