Nelson S Bond's "The Message from the Void" (as by Hubert Mavity) (short story, first contact, free): Is the most basic assumption of SETI wrong?
Both humans & Martians have been running their equivalent of SETI, looking for life on other worlds of Sol.
OK - comparison with SETI is only approximate; characters in this story are actively seeking contact with intelligence on other worlds - by sending trivial, most natural, puzzles & listening for their solution - like in Hal Clement's "Longline".
Only both sides are conditioned by their own prejudices!
Fact sheet.First published: Dynamic Science Stories, February 1939.
Download full text as part of the scans of the original magazine where it first appeared.
Related: Martian fiction; Tuesday Classics.