So the indicators are stealing earth because they have none of their own. The clear plastic cylinder thing on the left is stuck to its loom. Prise something thin in between, very carefully, then wd40 or something, then slide it back. Disconnect the plug, give it a good clean.
I use electrical circuit board cleaner, but deoxit seems to be the go. Whenever I ask for it in a shop, I get looked at funny, I say don't look at me, l don't know what I'm talking about either.
Clean it as best you can, then dry it, put it back together. Now test your indicators, horn and light switches. Then do the right side, then test your switches again, especially on your right handlebar.
On the frames central bar, on the left, you will see a bunch of brown wires bolted to it. Doesn't matter if they look good, scrub them, spray cleaner on them, dry them, clean them real good. Clean each one separately. Test your switches again.
If lucky, your indicators will now work properly. Look for any exposed wires and wear spots. Then clean all the other plugs. Look on the left, for the wear spot mentioned earlier. There should be a rubber grommet to protect wires exiting the relay box.
With your fingernail flat on the horn relay and a short press on the left indicator, you might feel a vibration, then that is where the noise is coming from. The left indicator is trying to steal earth from the horn, but failing, good.