dc5 strange noise when its wet

[slidetaker]

i doubt it would be engine mounts
its def an electrical problem
my voltage meter on my head unit drops from 14v to 11v when the problem happens and it only occurs during heavy rainfalls

so we have lost of power, knocking and gearbox vibrating and under the seat too.

---Do they all happen at the same time?
---How long will they last from the second it occurs, I assume it only happens during acceleration?
---Does the voltage keeps at 11v during the whole occurrence of the symptoms?
---Do dealerships check whether it registers any DTC?
--- Does it happen to both manual and auto box?