"A rift in the lute" nghĩa là gì?

Ví dụ 

The arrival of the mother in-law in the family proved a rift in the lute.

I hope this bit of rust isn't a rift in the lute and doesn't end up damaging the whole paint job.

The country may favor this economy, as was claimed, or it may not. But no matter where it stands, there seems to be a rift in the lute of the administration's peace. 

Cinderella has married her Prince Charming and has settled down to the aforesaid happiness. But there is a rift in the lute — and it is Buttons. Willing fellow that he is, he’s always worshipped Cinderella and at one time even hoped that she might be his but of course you know all that! Now, he has become something of an embarrassment, for he knew her long before she made the big time and is more than willing to talk about it. Obviously, he’ll have to go!