When I walked up to the client’s computer, I noted that it was on and running fine. When I asked what the problem was, she told me “It makes this horrible loud noise when it starts up!”
“From the speakers or from inside the machine,” I asked.
“It’s coming from the speakers, but like nothing I’ve ever heard!”
I restarted the machine and was greeted by a blank screen and three long tones, followed by four shorter ones. Then the process repeated. After five repetitions of this, the computer started normally.
I began to pull cables, and once I yanked the printer USB the sounds stopped. (Shocking. It’s NEVER the cable!) I tried the keyboard and mouse in that same port to make sure it wasn’t the actual slot, and had no problems. It seems this beep code refers to a malfunction USB device. Just swapping the port may help, otherwise replace the cable or device.