Thanks AppU for your thoughts.
Got the car inspected with a trust local mechanic and he recognized the problem at once. TASS is closed today due to local festival. Fortunately, nothing serious happened to the engine.
Engine guard is pushed upwards by the collision with the rock and engine vibrations are resonating with the guard. Guard is pushed down to its original position. BUT, vibrations still felt. Narrowed the problem to the vibrations at the right rear side.
Bent over to see the culprit and
That rock rolled from the front to back and dented the fuel tank.
Further, exhaust pipe is bent which is touching the underbody making rattling noise. I didn't mind about the engine guard, exhaust bent but looking at the fuel tank is making me seriously frustrated considering my vehicle is not even 1 month old. I'm regretting now not to accompany my younger bro for his ride (he is learning how to drive).
I'm considering replacing the diesel tank all together though my mechanic is not advising me to do so and he said it is just fine. But, I do not want to get stuck on road side with a hole in the tank in future. Guys, any idea how much does it cost to replace the fuel tank?