Very common problem with this era of Bally games, yes, the buzzing changes pich as the high score alternates, & does tend to get worse as the game warms up too, annoying.

Replace.the caps on the sound board may fix it, or for a quick fix, if you simply loosen the two bracket screws on the sound board a bit to disconnect the ground contact from the bracket to the board, this usually stops it. I have had mine like this for years, has worked fine. In the end I put a small section of cardboard in between the board & bracket as a buffer & tightened the board screws back up.

Board gets a ground connection to function from the a plug connector wire, so breaking the board to bracket ground connection doesn't seem to create any problems.