He has a 1995 Spanish ST1100AS where S is the year code.
I think the ABS light should come on steady and not go out until about 8 km per hour. The blinking and fault code mean a defect, I think,
The buzzing is probably a pump operating in a modulator. It is not normally loud compared to engine noise, but maybe Jorge put the microphone near the pump. If so, the buzzing sound is good news.
Where to start‽
Owner manual after 1991 for how ABS lights should light up, go out, and not blink.
Honda service manual after 1991. If after 1995, read only the 1992 to 1995 section.
Make sure he knows procedure for getting correct fault codes and clearing out the older codes.
Then post results here.
For a parts list, visit
www.cmsnl.com or
www.st-1100.com . On the latter, select Menu, then Parts Fiches.
Get translator as needed.