Stone deaf is an expression meaning completely unable to hear.  Stones cannot hear.

Hard of hearing may refer to a person with partial hearing loss.

An ear trumpet used to be used by people with hearing loss to amplify speech.  Nowadays there are much smaller hearing aids.  (At one time they were called deaf aids as they helped deaf people to hear.)   Deafness is an invisible disability of which I am particularly aware.  I know many people who are affected by hearing loss.  I have also known a number of teachers of deaf people.

A tell-tale tit is someone who reports the (usually bad) behaviour of others.  In the Bible Joseph is recorded as having behaved in this way and antagonising his brothers.  Genesis 37:2

Telling tales is what a tell-tale tit is good at.  Story-tellers also tell tales.  Some tales are true and others are embroidered or completely false (or fictitious).

That would be telling… is a way of avoiding answering a question.

Hearsay is a word for rumour – something, which has been heard and repeated.

To have a go at someone means to nag or criticise them.

The plot thickens means that a mystery is becoming more difficult to solve or someone’s motives more difficult to guess.  This is the sort of plot, which is the outline of a book not somewhere to plant vegetables.

By the bye is the same as by the way incidentally.

Baying at the moon is something dogs and wolves do.  The idiom means “railing at those in authority” according to Brewer.  It is rather ineffective.

Tell it not in Gath!  This is a reference to the town, which raised Goliath (killed by David, the shepherd boy 1 Samuel 17 ).   In 2 Samuel 1:20 there is a warning not to tell the people there or in Ashkelon, another enemy stronghold the news of the deaths of King Saul and his son, Jonathan.