Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
That's a clear sign of a sticky or jammed shutter mechanism.
It's quite delicate, and as easy to make worse (if possible) as better with ordinary tools and means. Having it be sticking, means the camera has to be taken to a camera shop of good quality that can and does fix such problems.
Being a Nikon camera, it needs a Nikon Authorized Service Center. Where are you located, please? by zip code.
Only Nikon themselves (factory repair, essentially) can help with this product's problem.
and fill out the form there, to order servicing for your camera.
This is Nikon's central repair page in case you need it: