Little nervous after the Kick's purchase

Bought XVD Pre kicks this month (sep 2019). When I took the car out first time from showroom, I realized a vibration in 30-50 speed. Couple of days later called Nissan showroom people. They asked me to bring the car and we went to the service center for checking. The technical team kept my kicks for a day and did all testing, they found the issue, but not able to find the core point that causes this problem. Now they asked me to drive for 1000 km and asked me to bring the kicks after that. The problem is still persists after 500 km. But I am feeling little nervous now.