Tim !
If you are able to determine which relay is buzzing and where it is located eg. in the back box/light box, under the playfield, on the coin mechanism as mentioned or on the base of the machine cabinet?
If your lucky, the relays will have a small label beside or letters e.g. R, AX, S,..... on the relay.
The spinner contacts or roll overs switches under the playfield are worth checking as they may be closed or not adjusted properly, and causing a relay lockup.
