Mine does the same thing, both the relaxed one and the hyper one will both scratch at the glass. Starts at about 9.30 in the morning (hell on a saturday morning when you've got a hangover
) and continues till they start settling down go to bed about 3.30 in half hour bouts (they like to have a warm inbetween). I tend to think of it was teenagers burning off mad energy.
If you can get them try coaxing them with nisturtun (god knows the spelling of that) flower or dendelion flowers
Good luck honey