windscreen causing oscillation?

[Aussie_imp]

How many miles on your rear tire?
There is a decent chance that the screen is not causing the oscillation when you take your hands off the bars at all. That is a classic symptom of cupped tires, and if it's the case, the oscillation will stop when you replace or re-balance the tires. If they still have a lot of miles left on them, just be aware, take it easy, and maybe keep your hands on the bars until you get the new tires.

But it's generally been my experience that tall screens are worse at speed. I'd rather have the steady, uninterrupted airflow hitting my helmet, than the chaotic turbulence whacking my helmet around behind a screen.

Thanks for the tip mate. I checked without the screen and the bike runs true with no issues so I'm pretty sure it's the screen on this occasion. Cheers.