This one is similar to an earlier malaphor, “put your shoulder to the grindstone” (posted July 20, 2012 – see body parts in index), except it mixes “keep an ear to the ground” (devote attention to watching or listening to clues) and “keep your nose to the grindstone” (work hard and constantly). While these two idioms have different meanings, they both express diligence in an action. They also both have the word “keep” in them. Finally, adding to the confusion are the use of body parts. Body parts are a common source of confusion for some reason, particularly if they are in close proximity – in this case, ears and noses. An amusing aside – I heard this one from a supervisor who was giving me advice.