Drive chains on brand-new bikes tent to be adjusted to the point where there is not enough chain slack.
Don't blame anybody at the dealer because that's how the bike rolls out of it's shipping crate (and, frankly, most dealers intentionally put the newbies at the bottom of the dealership totem pole in that "entry level" position - prepping your new motorcycle for you).
Also, most riders, too, will be constantly adjusting their drive chains, all riding season long, always removing needed chain slack.
Get down low and point a flashlight up from beneath the swingarm pivot, just behind the front sprocket.
If the chain is way too tight, the chain will grind the forward edge of the chain slider away and continue gnawing through the swingarm, itself.
The more your rear suspension sags during this condition (lowered rear suspension, always carrying a large load of camping gear, etc.), the faster this will happen.
If this checks out OK, it's coming from somewhere else along the chain's path.