There are dozens of posts on the engine mechanical noise level on the NC. There is a considerable amount of “normal noise” or character built into the NC.
One test, at idle in neutral pull the clutch lever..........does the noise change ? The primary drive and transmission gears create a considerable amount of the noise.
Many of these prior noise discussions were on brand new bikes with very low mileage.
Many of the posts have video and audio clips of the noises.
There a few prior posts where this was discussed.........some with engine disassembley........only to find no problem.