People who are loud and talk a lot usually have nothing of substance to say. This contrasts with "Still waters run deep." Other versions are "Shallow brooks babble loudest" and "Shallow brooks are noisy."
If someone beats the daylights out of another person, they hit them repeatedly.
('Knock' can also be used and it can be made even stronger by saying 'the living daylights'.)
If you are caught between a rock and a hard place, you are in a position where you have to choose between unpleasant alternatives, and your choice might cause you problems; you will not be able to satisfy everyone.
If something like a sports match or an election is a cliffhanger, then the result is so close that it cannot be predicted and will only be known at the very end.
'The grass may be greener on the other side but it's just as hard to mow' is an expression used to mean a person's desire to have that which another person has in the belief it will make their life easieris false as all situations come with their own set of problems.
If you let the dust settle, or wait till the dust settles, you wait until things have become calmer or have returned to normality after conflict or a problem.
If people have/take/claim/seize, etc, the moral high ground, they claim that their arguments, beliefs, etc, are morally superior to those being put forward by other people.
If you would move mountains to do something, you would make any effort to achieve your aim. When people say that faith can move mountains, they mean that it can achieve a lot.
This idiom means that when people suspect something, there is normally a good reason for the suspicion, even if there is no concrete evidence. ('Where's there's smoke, there's fire' is also used.)