Year
Mileage
Last maintenance, what has been done.
Time since work done till problem started.
Can't guess without a few clues

I am not certain if I would suggest running and idling and getting video considering the severity of the noise?  

If it's a cam chain tensioner about to drop out this engine could be one crank away from destruction.  If we can assess the mileage and see that it is 10-15K or more (within the "inspect your tensioner" range), wouldn't the safest bet to be to open the case before doing anything?

As noted by the previous posts, can you first advise on the year and mileage and any maintenance and then we can suggest next steps (video or not).

If the cam chain tensioner isn't the problem(but you should check this first) and the vibration tends to lesson as engine speed increases it could be a loose flywheel ,we have seen a few cases where the nut backs off .

There is another possiblilty and that is the piston.
One of my bikes had sat for an extended period of time without cranking/starting, about 6-9 months.  When I did start it I noticed a small knocking sound but was having difficulty isolating where  the sound was actually coming from.  It still ran, and as the rpm increased it seemed to lessen a bit.  When I finally pulled the engine for a look I found the rings has rusted just enough to hold the piston briefly when I did finally start it.  At that starting sequence the rusted rings held just long enough to yank the piston sideways and cause a gouge in the piston skirt and that left a little deposit of aluminum on the cylinder wall.  I was able to remove that deposit and there was a tiny ding on the cylinder but I was able to just hone the cylinder and install a new piston.  It works just fine now and only cost the $$ for the piston.
The reason I did not bore the cylinder is because it was already out to 97mm, so no room to bore more.  Yes, fortunate.