The same comments as Renato,Peter and Linas.Its most likely a lubrication problem, possibly a bit of grit has got into the system,similar to window grating/grit problem.
As Renato said Gummipflege is a good idea on all the rubber, especially the inner thick seals around the frameless windows..by coincidence,Idid mine all round 2 days ago.
Another possibility -- there hasn't been a Lexus Reading van lurking around your house late at night?….....