Welcome to the site !!
That noise is what happens when the chain is too loose , its chain slap basically , you need to readjust it , its possible that the chain is stretched too far and that will cause the noise , but again , usually when the chain is too loose
The best way to adjust it , is to loosen the axle nut so its still snug , but allows you to slide the axle/tire back and forth with a little effort , then adjust your tension bolts (evenly) till you can just fit 3 fingers on the swingarm just behind the chain slider , you don't want to be able to spread your fingers , but it should not pinch them together either (it will basically be about 2-1/2") , then tighten everything back up making sure you have the adjusters even so the wheel will track straight and so it does not cause the chain to ride up on the sprocket teeth , then ride it and see if the noise is gone ,,,,, it should be..... , if the slider is worn , (usually it wears more on the bottom) , then check the swingarm for any damage , hopefully you caught it before it did any damage to the swingarm , especially around the swingarm bearings (underneath ...look for grooves from the chain) and replace the slider ASAP , as its the life blood of your swingarm , once it's worn thru , your risking swingarm damage .... hope that helped some....