Noise coming from gearbox area
 

I bought a 03 montero over a month ago and it was fine until once I hit a manhole cover that was depressed into the road at about 50 kph and a rattling noise came from the box but it immediately went away, today all of a sudden it returned but its staying. The noise increases with speed and has kind of a grinding sound as well. Any pointers would be appreciated! I saw on a forum that it might be 4wd solenoid but I still have to test that.