It's possible there's water in the discharge pipe that's leaking through your backup since, as described in the installation manual, the check valve should be located just below the PVC "T" that the backup is mounted to.
Regarding the constant buzzing from the charger, if it's the alarm, it usually indicates a problem with the battery. Per the instruction manual, I would suggest:
(a) Push alarm reset (max. 3 times). If condition persists,
replace battery.
(b) To silence alarm if alarm will not reset, unplug the charger
from 115V wall outlet, then disconnect the black lead from
charger on negative (-) battery post. Check battery. Replace
if necessary. Reconnect and refer to Installation (step 14).
If it is not the alarm sounding, I would suggest contacting Zoeller Tech Support at (800) 928-7867.