Many details required on this one. Transmission type for sure, check with windows down - is it coming from a particular side, could be a leak in the exhaust - could be there the entire time and you can only hear it over everything else while decelerating.
Juttering while driving - is it in the steering wheel or your butt? Do the noise and the jutter seem to be pulsing together, if at all?
Video?
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View my fuel log 2015 Micra SV automatic: 7.1 L/100 km ... 39.9 mpg (Imp) ... 14.1 km/L ... 33.3 mpg (US) ...