The game starts playing a short piece of audio on a loop. The switch matrix is clean and swapping in spare sound boards (with the game's own ROMs) doesn't help.

Sound loops over and over: reburn the sound ROMs even if they verify

Cause: One of the sound ROMs (AROM2) had gone bad.

Checks

• Swap the sound boards but keep the game's ROMs: if the fault stays, suspect the ROMs.
• Verify each ROM against the correct files.

Fix

• Reprogram (or replace) the faulty sound ROM; here AROM2 fixed it.

Games

• Rescue 911

Source: Pinball Repair help group!! (Facebook group)