[jama_]

I have permanent tinnitus and have this too, though it very rarely happens on its own. When it happens, for me, this sound is usually a signal to immediately change my posture when sitting in a chair.

When I reach flow, I tend to not notice until later that I'd now be sitting cross-legged, or that I've tucked one leg under myself.

That pressure tends to trigger the sound you describe after a while. I imagine because of bad blood circulation, though I have no idea why it's that sound signalling that for me.

[keybpo]

Same with me. It usually happens when I've been reading in bed for long and I unconsciouly get in a bad posture (neck). Correcting it, doing some shoulder and neck light exercices help but I've never associated it with pressure caused by lower body, mainly legs. Which it might as it also happens when I'm cross legged (and somewhat torso twisted) at the computer desk for too long.