Mount Range Hood

Mount Range Hood
How do you determine where water is coming from in a roof vented microwave and fix it?

I have a microwave to be mounted over a Range Hood and has a vent that exhausts thru the roof. I removed the old microwave but needed some items to install the new, so while the area sat empty, water began to occasionally drip down onto the stove below. A look in the attic revealed no apparent water and it seems to only drip on cold mornings, so possibly condensation?

I'm concerned that water will leak into the microwave blower motor and cause damage to it or worse.
I just bought the house and had a contractor work on the exhaust on the roof. Maybe this wasn't done properly, but it didn't drip down during several heavy rains, so I'm thinking that it isn't the roof pipe.

If you are in a cold region..... and with the vent open and the rush of heat unabated…… I would guess that it might be condensation.