Definitely a good idea to get a mechanic to look at it I'd say especially if you're worried.
The thing is if it is the clutch release bearing as I suspect then to replace it you will need the gearbox off etc so that's going to be expensive.
If you do need to get the bearing replaced and your clutch/flywheel are old or worn then it's best to get them changed at the same time rather than have to pay the labour again if/when the clutch goes in the future.
The bearing though could last thousands of miles before it finally goes, ...you'll know when it goes as your clutch pedal will more than likely just go to the floor & you won't be able to select gears.
If you do need a clutch/flywheel/bearing etc then don't forget Clark Motorsport, Tarmac Sportz, TORQEN etc on here can all help for more than likely less than the price of OEM equipment from Nissan.
Still let your mechanic have a look and see what he says ~ always difficult to diagnose problems over the net just described by noises/feelings.