I've noticed that my high beam is occasionally coming on without me selecting it.

2 different instances,

1. When using indicators sometimes high beam flashes on momentarily.
2. Occasionally when driving with lights on the same happens.

Any ideas for a fix? 

[Aye30]

Does the stalk feel  like it has play in it? Could it be worn? If it feels tight it could be wear on the actual switches. Normally the stalk movement is plastic on plastic, with a plastic  compatible grease, and the detents get a little wider over time.

300 000km so I suppose it's worn. No play yhat I can sense.

I guess a new stalk if it gets worse?

[Shambles]

Although it smells mechanical (sounds like the stalk to me as well) you can't rule out a twitchy BCM on these FD models. It's that old suggestion - disconnect the battery for 30 mins to rule that out.

Good luck.

[Richo80]

Very common for the stalk to be faulty. new stalk needed.