For some reason certain Notes suffer from malfunctioning PCV valves. Results in unsteady idling , bad starting strange noises. Not detectable on ODB2 diagnose. Might damage engine quite a lot. Had this once, reoccurring again. Get impression not only mine is affected. Poor design and quality again in combination with increased ethanol percentage gasoline and use of cleaning additives to the engine. Dealers suggest you exchange a lot expensive parts whilst it concerns this cheapo part which dan be cleaned also. Problem increases with unused vehicles during corona crises where these additives and ethanol get extra change to do unwanted effects. On trouble let your dealer check this first before anything else. Nr 1 obligatory.