Holding the button produces a loud buzz.

Flipper buzzes when held up

Cause: The plunger vibrating against the coil stop, usually from a rough plunger or stop, a loose coil or stop, a coil stop that has lost its magnetism, a worn link, or poor EOS contact (chatter).

Checks

• Check the coil and coil stop mounting screws.
• Look at the plunger end and stop face.
• Check the link for slop.

Fix

• Tighten loose screws; on slotted brackets, slide them to clamp the coil snugly.
• If there are no slots, add a large washer over the sleeve at the plunger end of the coil (not the coil-stop end) to take up play.
• Smooth the plunger and stop, replace a worn link or a non-magnetic coil stop, and clean and adjust the EOS switch.

Systems

• Williams System 3
• Williams System 4
• Williams System 6 / 6A
• Williams System 7
• Williams System 9
• Williams System 11
• Williams System 11A
• Williams System 11B
• Williams System 11C
• WPC Alpha-Numeric
• WPC Dot Matrix
• WPC Fliptronics
• WPC DCS
• WPC-Security (WPC-S)
• WPC-95
• Bally MPU AS-2518-17
• Bally MPU AS-2518-35
• Stern MPU-100
• Stern MPU-200
• Bally 6803
• Gottlieb System 1
• Gottlieb System 80
• Gottlieb System 80A
• Gottlieb System 80B
• Gottlieb System 3
• Data East CPU Version 1/2
• Data East CPU Version 3
• Data East/Sega CPU Version 3b
• Capcom
• Electro-mechanical

Related tips

• Flipper buzzes loudly while the button is held
• Flipper buzzes and vibrates when held
• Flipper machine-guns when the button is held
• Weak, chattering or buzzing flipper: end-of-stroke switch
• Flipper button sticks
• Flipper flutters when held up
• Fliptronics: flipper will not hold up (flutters)
• Flipper weak: worn plunger, coil stop or sleeve

Source: Pinball Machine Care & Maintenance, Bernard B. Kamoroff (Bell Springs Pinball Alley)