I also noticed the same thing the first winter with my new '13, it would generally only happen when quite cold out and generally backing up and turning the wheel. It took 2 trips to the dealer because the first time they said they couldn't hear anything as of course the day I took it in, the temps had warmed up. The second time they ended up replacing several front end parts but as it was under warranty I'm not exactly what all they replaced, it was free and after I didn't hear the noise. About half way through the next winter the sound came back but not as loud. I still hear it occasionally to this day but basically ignore it. Not sure there is anything to grease but I guess it wouldn't hurt trying.
Since it sounds like your Leaf is no longer under warranty I'd first see if there is anything to grease, if not I'd just drive it until it gets worse and in the case of mine it doesn't seem to be, just somewhat annoying for such a new low mileage car. I never had such problems with my prior 2 Toyota vehicles and I sure with Toyota had made a BEV available in my market but alas no they wasted(IMO) so much time on fuel cell vehicles other companies like Nissan overtook them and now they are scrambling to catch up
2012 SL purchased used 2/'16
2013 S w/QC purchased new
Juicebox Premium 60a L1/L2 EVSE, Ebusbar 16a L1/L2 EVSE
'12 EVSEupgrade'd 20a L1/L2 EVSE, '13 EVSEupgrade'd adjustable 6-20a L2, 6-13a L1 EVSE
Zencar 13, 20, 30a L1/L2 portable EVSE
GE Durastation 30a