Holding a flipper up makes a loud buzz.

Flipper buzzes loudly while the button is held

Cause: A worn coil stop. EM coil stops are made slightly magnetic, which damps the AC vibration of the held plunger.

Checks

• Check the coil stop face for wear and looseness.

Fix

• Replace the flipper coil stop.

Systems

• Electro-mechanical

Related tips

• Flipper buzzes when held up
• Gottlieb flipper coil windings (power/hold)
• Flipper stays up after the button is released
• Shock from Gottlieb metal flipper buttons
• Flipper coil burns or solenoid fuse blows: EOS switch
• Rebuilding an EM flipper
• Which games have zipper flippers
• An EM flipper coil is two windings

Source: Repairing Electro-Mechanical (EM) Coin Operated Games to 1978, Part Two, Clay Harrell (pinrepair.com)