We set up Elly plotting to murder Mike by having her use John as a stand-in for every evil working person who's ever tried telling her the Evil LIE that she's gotta put up with a little noise during the renovation process.
(Strip Number 1331, Original Publication Date, 9 August 1988)
Panel 1: As Elly tries to have a talk on the phone with Carol, she tells her to hold on while she addresses the issue of someone hammering something.
Panel 2: When Elly asks John what he's doing, he says that he's putting up the wainscoting.
Panel 3: She reminds him that she's on the phone while he says that he's gotta get this done.
Panel 4: Instead of asking him if he can maybe wait a few minutes, Elly reminds us that she's not especially bright by asking him to hammer quietly.
Summary: This example of Elly not being all that aware of how things work leads into the real point of this: making sure that Mike gets into even more hot water when he gets back from camp. Also, today's version of John is a stand-in for every workman who's ever punctured Lynn's fantasy capsule by making noise when she's trying to commune with the muses.