"*Knocking sound, in Joyce's ""Ulysses"" (longest palindromic word in the OED)" crossword clue

Let me guess, you have been playing a crossword game and got stuck on the clue "*Knocking sound, in Joyce's ""Ulysses"" (longest palindromic word in the OED)". Well, you have come to the right place to find the answer to this clue.

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