I've been trying to find an answer to this problem for over 2 weeks
now.

Here is the situation:

2 newly installed panasonic 80 cfm bathroom exhaust fans(the kind that
fit in a 2x4 joist space) in two different bathrooms. These fans have
their own internal flapper.

Bathroom 1: 8 x 4 x 8
Bathroom 2: 8 x 5 x 8

I'm using 3" sheet meal ducting(the kind you have to "snap" together)
going horizontally out the side walls instead of going straight out
the roof. They duct out to exhaust hoods which also have a flapper on
them. I also have put insulation on the whole duct run.(not tried
putting insulation on the fan housing yet due to mold concerns.)
The duct runs are about 4' each from the exhaust fan and slope
downward from the start of exhaust fan to the wall, so you would think
condensation would just drip out towards the wall. You can go outside
while the fan is running and seems like its pushing out plently of
air. The fans are mounted in between the shower and the vanity right
above the toilet. The are mounted at a downward angle since the
sheetrock ceiling has a downward shape that matches my open beam
ceiling slope patter.
My whole house is all open bean ceilings, there is no attic. The duct
run is made above newly installed sheetrock and the open beam
ceilings, with a 4" space between the sheetrock and the open beam
ceiling. My open beam ceilings are vaulted going downward towards the
side wall, so the ducting runs down the similar open beam downward
slope. The ducting is not bent at all in the larger of the bathrooms,
and has a slight bend in the smaller of the two bathrooms going out
the side wall.
When I take a shower in the smaller of the two bathrooms, after about
5-6 minutes, condensation starts leaking from the fan housing thru the
grille. I thought it was due to it being pretty cold outside, but
today was fairly warmer and the same results happended.
In the larger of the two bathrooms, it takes slightly longer to
condensate when taking a hot shower since its a bigger room, but it
happens in that bathroom as well.

Can anyone shed some light as to how I should go about solving this
issue, as I am out of ideas.

thanks,
Isaac