Holding the button makes the flipper chatter with a loud buzz.

Flipper buzzes and vibrates when held

Cause: Open hold (fine) winding, usually broken near a lug.

Fix

• Resolder the broken fine wire if you can find it; otherwise replace the coil.

Systems

• Williams System 11
• Williams System 11A
• Williams System 11B
• Williams System 11C
• WPC Alpha-Numeric
• WPC Dot Matrix

Related tips

• Flipper buzzes when held up
• Flipper flutters and will not hold up
• Pre-Fliptronics: flipper flutters while the button is held
• Upper right flipper only buzzes while the magnet holds the ball: failed opto-isolator
• Pre-Fliptronics flipper coil smokes when held up
• One flipper does not work at all
• Weak flipper: dirty cabinet button
• Weak, chattering or buzzing flipper: end-of-stroke switch

Source: Pinball Machines: How They Work & Troubleshooting, Norbert Snicer