Clown fish mating or something?

[Beau B]

i have 2 clown fish i purchased at the same time about a year ago one is a little bit bigger then the other which tells me its the female. Their doing this weird rubbing on the glass in the corner that looks a lot like their mating (laying eggs) but i do not see any eggs. If you look on youtube for clown fish breeding its almost like what mine are doing except mine are adding a little more shake to it 1 will shake on the glass then the other 1 will come along and shake in the same spot but theirs no eggs or anything they'll do it like 2-3 times then stop swim around and do it again they've been at it for almost 30 mins now. any advise helps