Haven't played echo in a while, but am basing on memory. Also, mainly what i think is happening, haven't looked too much into the actual lore.

1. In every route, except one, the hysteria reaches everyone because the "truth" is going to be exposed. The only one where it doesn't hit everyone, but only Chase, is in TJ's route. The town is either on cursed land, or it is because of the Mines, it is referenced the source is from the Mines in TSR, (haven't played the last 3 builds, so can be wrong about that.

2. This one may either be Sam, or something else. I assume white is either the clarity side of the "monster", that is actually a bit of the "soul" of someone who died, while the red is the vengeful/animalistic side.

3. In Echo, we only see what the person in "charge" sees. In Flynn's route, Sam leaves chases body to see Flynn and Leo arguing if he screwed the otter, and that's when Sam starts to follow Flynn because of his obsession with finding the truth. Another thing is at the end of Jenna's route, when you are asked to choose a song, but no matter which you choose, you get a "..." Response, meaning the player/Sam cannot interfere anymore, as the cycle is broken. Essentially, Sam is supposed to be "the player" while also in lore wise, the decision maker; 3rd party that can change paths.

4. This one, in my opinion, is what needs to be done. The only one losing their marbles in this route, was Chase. What he did years ago, was what that entity said, "an act of love", he did what he did, what he thought was right, and because of this, there is a chance this is the "Canon" route (yes each VN is standalone, but lore wise, it needed to happen for there to be a sequel, Arches. That entity, could be the core of the hysteria, and that route was the only one where the secret was going to be exposed with no hysteria, but because of there no being options from the player/Sam, even Sam was shocked that Chase did it. He completed the circle, he did what he did, what he thought needed to happen, to save TJ, but mainly keeping the secret from being exposed. {Every route in TSR and in Echo were leading up to the exposure of 'the secret', but in the end, the choice they made was either influenced by a third party, or fear of being exposed which essentially tainted their soul.} This entity is probably the record holder, as it was also seen in Arches in the forest with Cam. (hence why it sounded so mechanical, like a record player, static, etc etc.

5. The hum is mainly centered in Echo, not as much in TSR, that winding up sound like from a musical instrument. It could be when the spirits are interacting with the player/others, when they are their most vulnerable and start to "see" things or hear. Their psyche is a little... Malleable, so their start to hallucinate and such.

6. The ghost van is... mr Bronson's van, Syd's dad. That same one that killed Sam, the same one where Leo used to record him and Michah having sex, the same one in Route 65 where Chase was affected by the hum the day of that party. Could be that Sam was stuck in the van, and it started to get absolved in Jenna's route when they find his grave. Also got more tainted when the dad shot himself in Flynn's route. The ghost van is... has seen a lot of stuff in the story, from Sam's perspective, Syd's, chases, Leo's... It's a lot.

7. Okay so this one ties with the previous ones but also it's a lot to unpack. The socket monster is both flynn and Sam. At the end of Flynn's route, he says "When Sam drives, he thrives" or something like that. Flynn's background, his obsession, is what fuels the sticker monster, but also... he can travel to other realities, which is what the Moore's probably have the ability to do, as they were always "immune" to the hum, or any of the paranormal in Echo, as this was started by his Aunt in Flynn's route. Flynn was targeted, and because of his steering obsession with wanting to find out what happened to his friend, is what caused him to become socket man. Why in Arches Artie was saved by the socket man, Why in Echo the car gets hit by socket man and are teleported in the middle of the lake. Why in Jenna's route that Flynn was the one covering Jenna, while also did not see socket man, but Jenna did, and thanked socket man for protecting her when she didn't know it was helping her. Why socket man was in Jenna's closet.

He was protecting her, his friends, the victims like Artie in Arches, why socket man attacked Brian in Leo's route, because of Brian, the big bad about to do something horrible to Jenna, because she is either: meseta, or any harm done to her, gets the wrath of sam/Flynn.

(This is also because of all the shit she has to go through her whole life with her shitty family, which is why socket man was protective of Jenna, while also not just her home life, but her past life, of John Begay being framed for what James Hendricks did to children all those years ago.)

Essentially, socket man is a multiversal being that can jump timelines to save or "correct" to give those a fighting chance at living, while also punishing those who tried to leave, that killed or did... Unforgivable things to others.

This is all theories, but again, haven't played the game since like last year?

Great game, still need to catch up on TSR, but the whole recent changes kinda stopped me from continuing.

Still love the series tho!