When should have banquo been suspicious that Macbeth was trying to kill him?

I might have clued in when Macbeth was asking questions about what Banquo was doing before supper,

Macbeth’s not so subtle questions,

"Is ’t far you ride?"

"Goes Fleance with you?"

At the same time Macbeth is acting all worried that Banquo might not make the feast. Macbeth needed some acting lessons!