I may be speaking out of turn and without all required information, but it's not unheard of for there to be a little air that makes it's way through the system after a flush/fill. Driving it and turning the wheel back & forth will usually take care of it. Definitely check the fluid level first.
With that being said, if it goes on for days & days, it's possible a suction line has an air leak and is re-introducing air into the system. If that's the case, you'll have to have them find the leak and tighten the connection or replace the hose.
2012 Frontier CC SV 4x2