Passenger window 'twitching' up and down

[somerled]

My 1998 2.5 Boxster has developed an issue whereby when the passenger side window is fully up or near the top of the window frame, is starts 'twitch' up and down only slightly (maybe a few mm) but very quickly and repetitively until it drains the battery.

The only way I can seem to stop this from happening is to put the window down a bit which means I can't leave the window up when out, parked, or in the garage. Does anyone know what might be causing this and if so, what I need to do to stop it? I imagine it might be a faulty switch somewhere. The windows also do not drop anymore when the roof latch is released.

Thanks in advance for any help.