oil pressure light and buzzer on

Just bought this little 1985 golf diesel converted with a 1996 1.9 engine non turbo, with about 100,000 miles. Runs strong, starts right up even in cold but there is a bit of rattling from down low somewhere in engine and the oil light comes on now just in past few days since I have been doing some major climbing from 5000 ft to 8000 ft. in 20 mile stretch. When I am in 4th gear at the steep part of the climb the light and buzzer goes on until I shift down to 3rd and it goes off, but it also seems to have less power for a moment. The oil pan has a big dent in it which did not seem to bother anything, but recently with the steep mountains the light is becomming more incesent. Could the oil pump have interference from the dent in the pan? I would appreciate your input, thanks