I have the exact same problem, with the freelook option disabled.
The problem exists with all kinds of vehicles, land and air and seems to occur mostly after playing for a long time (several hours) on the same server. The only solution I found so far is re-joining the server.

Once the bug shows up, the view also shows weird behaviour in other situations. For example as a passenger in any vehicle the view zooms in and out in quick succession or when on foot, the weapon is shaking weirdly (too quickly, but not much) every few seconds.

So far i only noticed the issue on king of the hill servers (which is the only scenario that I play multiple hours on the same server)