I am back trout, don't worry !

But for the bike. Which one i know pretty well I can say that the rattling comes from raised back wheel. Thats normal.
Rattling during driving comes from loose chain - thats also pretty normal - tight it up to normal slack ( it is given on the chain guard).

The humming noise. well i am not 100% sure, but it pretty much comes from front chain guard - guide ( the the 28 on picture above). The thing is that the first sprocket is 1 tooth smaller. It is right sprocket for that chain, but it's smaller. And as the guide is too big for that the humming noise comes when chain is dry and touches the guide probably.
The chain probably can not be stretched as it has never done even 10 000 kilometers, I would say more like 5000 most likely and it's DID chain.

The second thing is when you ride your bike on center stand you probably want to do that when engine is warm, and not use choke. because on choke the engine is not so smooth, and using not smooth engine on chain transmission which has slack - well i just say it's not the best idea in the world.

Ow and i forgot before: Clean the chain! It can rattle because it's not running smooth, as it is just not clean enough - the chain is not bending evenly everywhere. But do NOT use benzine while cleaning the chain - you will ruin the rubber O ring or Z ring sealing on chain

 

What happens if you remove the chain guide from the front sprocket, that you don't need?
A video is a video and it's not like being there, sounds like a sloppy chain.

One more thing, you can trash a new chain quick without proper lub and shifting in the red zone.