Since the knock gets louder "under load" (gas pedal input), then I suspect cheap low octane gasoline causing "detonation" (knocking when applying gas pedal input). Run your VX to near bone empty, and then put in a full tank of high octane "Premium" grade gas from a reputable brand (i.e. Chevron, Shell, 76, BP, Texaco). Never, never, use ARCO (their gasoline totally sucks).
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