Note to Twelfth Night, 2.5.64-65, "Though our silence be drawn from us with cars, / yet peace."
It's clear that Fabian wants Sir Toby and Sir Andrew to hold their peace, so the joke on Malvolio may proceed. Fabian may be parodying the importance of the silence he wants, as speech, not silence, is "drawn" from a person, who is tortured with two cars (chariots) attached at opposite ends a person, accelerating in opposite directions. Maybe Fabian is being witty, or maybe the excitement of the moment twists his words.
Malvolio reading letter while Sir Toby, Sir Agnew, and Fabian watch