How to Change the Startup Chime on an Intel Mac
In this video, I go over the process of changing the startup chime on any pre-T2 Intel-based Mac. While the process is actually quite simple, most of the later machines do not allow the OS to write to the system's SPI-ROM, making the use of an external EEPROM programmer necessary. However, any Early-2008 or older Mac, or 2012 or older Mac Pro, should have no issue writing to its SPI-ROM from the OS.
Things you'll need:
UEFITool (old-engine version): https://github.com/LongSoft/UEFITool/...
CAF ROM utility (for pre-Big Sur BootROMs): http://dosdude1.com/apps/caf-rom-util...
ROMTool (for dumping/flashing SPI-ROM on supported systems, ZIP password is "rom"): http://dosdude1.com/apps/ROMTool.zip
GUID of audio in old BootROM: 1F9CABF9-3F3C-4CFF-AED8-5FDF745A0DCC
GUID of audio in new BootROM: 03C70B0D-67E6-5C16-8E57-312DF246A961
CAF conversion command: afconvert -f caff -d ima4@44100
Original dumped boot chimes: http://dosdude1.com/sounds/macchimes/