Ok so again this is all my opinion of what i think could or might happen WARNING i dont know if this actually happens so *****SPOILER ALERT****** 

Ok so in the first Stranger Things season four teaser you hear and see a clock strike you make think that this is the first time you hear and see it but its not. In Stranger Things season two episode four when Hopper digs a hole into the tunnels in the upside down, as he looks out towards the tunnels as the screen turn upside down the screen goes black and you hear a clock strike. I think this was a symbol/sighn that it would only be a matter of time before the upside down took over hawkins 

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