A Bunch of Questions About the Ears, Hearing, and Tinnitus

Hi, I'm currently in a bit of a phase where I'm trying to find out anything I can about what could be wrong with my ears, and therefore I tend to end up with a lot of questions. I hope that someone here can help me find some answers.

For some background, I have mild tinnitus in quiet places that mostly scales with sounds around me, so the louder the environment, the louder the tinnitus, and tends to stay that way for some hours after exposure. Masking doesn't work because of that, but it is mild and I barely hear it most of the time.
I also have hyperacusis, mostly for quiet to moderate sounds. In short, train stations are fine, listening to music on my phone on the lowest volume is uncomfortable.

Today I also noticed a low tone in my tinnitus that I can only hear in very quiet rooms. Something like what you would hear when you put a shell to your ears.
I have no knows cause, and have had it for 4 years or so. The ENT does not know either, and I have some spray for ETD, which hasn't helped, besides opening my ETs. It is very unlikely to be noise related, I have always disliked loud noises and avoided them.

Alright some questions:

• How does ETD cause tinnitus and related stuff? From what I know about the ear, how can ETD influence the inner ear in any way and cause tinnitus (assuming it does that to cause tinnitus)?
• How does wax buildup cause tinnitus? Or is this just like 'rumbling' tinnitus, rather than ringing, in which case I get how it would do that.
• Sometimes I randomly hear what I think is my eardrum make some movement, what could cause this?
• Does the Eustachian tube do anything besides equalize pressure and perhaps help with fluid during infections?
• Can posture affect the Eustachian tube? When I do chin tucks my left ear pops sometimes. Could ETD be caused by forward head posture and hunchback posture?
• When I swallow, yawn and when I do it deliberately, I can open my Eustachian tubes (I think this is what is happening anyway) and I hear a click. I can do this several times in a row, so it is not just when there is a pressure built up, and if I do it deliberately several times, swallowing does not do it for a while (some number of minutes). What is happening here, what makes the clicking sound? It sounds a bit like ripping a few strands of Velcro, a few somewhat high pitched sounds. Hard to describe.
• What is fleeting tinnitus? Does it mean hearing damage? It happens to me somewhere between once per day to once per month, depending on how my ears are doing.

Sorry if I'm being annoying with all these questions. I rarely ask questions in general, but I'm not going to be able to find this out on my own.

Thanks in advance.