You hear constant creaking because it's a old, poorly maintained castle that is actively falling down. With numerous creatures walking about.
Have you ever been in an old wooden house like that? They do creak.
It's not because the main character is plastered.
Dang Wooden stone castle! with wood support beams that sound like an entire wooden house is creaking!
It is more that the sounds often come as... a bit overblown... Sometimes the castle sounds like it is a cave that is collapsing in the distance.
Sure wooden support beams can creak... But it is sometimes a bit ever present. (if half the noises the game makes were real...)
"It's not because the main character is plastered"
Ehhhh... Some of it kind of is... Atleast the game has plenty of events that only make sense if you assume something else is going on as opposed to this just being a really old or badly kept castle. Like the dust devils.
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Goodness I should state I am not trying to poop on Amnesia... Though I am CERTAINLY not talking like that isn't what I am trying to do... so sorry about that.
I am just a bit interested in how sober second thoughts shows the game's seams. Which its major seam atmosphere wise, is that it REALLY pushes it. It kind of makes me realize why some people don't find watching it scary to a degree... Because it is kind of unreal. Almost like you are in a dream and these are only things your character THINKS is appropriate for the situation.
(actually the reason why is because the game relies heavily on putting you in the character's shoes. The majority of the tension comes not from the enemy design, outright horror, and visuals/sound design... but mostly with how it interacts with gameplay. SURE you can handle the dark, but it kills you. Sure the enemies aren't that scary, but even looking at them kills you. Sure the castle is excessive, but you are at its mercy as far as how you will approach any situation and DESPERATE to get any leg up. This isn't a flaw, it is just how the game's horror works, it would be antagonistic to its design if it was quiet with loud popscares every little bit)