If the flasher make a noise when the RHS indicators are used it probably means that there is power going to the flasher unit from the stalk switch.
It could be a faulty pair on contacts in the flasher unit, but probably not. It sounds like the path from the flasher unit to the RHS bulbs and then to earth is broken.
You could try swapping over the left and right bulb feeds from the flasher unit to check that.
Also put a meter to the RHS feed line at the bulbs to see if you are getting power.
