Every few seconds something from driver front side goes pssshh. Not particularly loudly, but enough that you can hear it... air leak? Noisy black one

Is your air compressor running at the same time? If not, I doubt it’s a leak, maybe something moving which sounds like a leak. 2019 5.0 SC SVA (Current)
2012 5.0 SC AB. Sadly written off by a campervan
23 plate Focus ST (Current)
1942 VEP Ford GPW Jeep (Willys) (Current)
1943 Whites M16 Halftrack (Current)
16 plate Eurofighter Typhoon, 2 x Eurojet engines with 20,000lbs thrust each. 1380mph

No my mechanic just noticed it when the car was sitting still on idle. We were actually trying to work out what the exhaust rattle was  Noisy black one

The valve block for the front suspension is in the offside front wheel arch so it will more than likely be the system self levelling. Mine usually hisses and clicks a couple of times after I park up.

Thanks guys Noisy black one