Noisy, weepy RO

My RO unit (RO Ultratec, 3 canisters, 2 membrane cylinders) makes an
intermittent buzzing noise, and also seems to be "weeping" (not enough
to actually drip) from most of the plastic water lines. I replaced the
filters (not the membranes; system is only 7 months old), but I still
get the buzzing and the weeping. One membrane cylinder is connected to
a float valve for the sump, and the other is for water changes etc.
The cylinder connected to the float valve shows constant pressure, even
when the float is closed, but the other cylinder only shows pressure
when the valve is open (making water). Any thoughts on what is causing
one or both of these problems? I have no manual/info. on the system,
and no longer do business with the LFS that sold me the set up.