TF10 uses balanced armatures, so they are not meant to have driver flex.
I'd say distortion (IEMs do have distortion)... I don't think you understand what driver flex is... Driver flex is caused by air pressure in your ear. It prevents the driver from moving (EG, keeps it in a flexed position). The real only way to force a popping noise (be the same at the same point in the song) with driver flex is to move the driver at the precise time with precise movement at the same point in the song every time... The chances of that actually happening, well, you should play the lottery (better odds) :p Unless you can think of any other way for driver flex to occur... What IEM are you using?
Not reading all of the thread, but this caught my eye.
My left ear is fully blocked. I can't blow through it or anything. I may have to get grommets, but the thing is, when putting in my IEMS. my left driver "Pops" and the right one doesnt. Obv, this is the driver being pushed into a closed space, but it is what it is.
Horrible driver flex on my Brainwavz R1. On the left side only in my case.. I think its just down to manufacturer imperfections with this model.
I've had a little bit of driver flex in the left channel of my monoprice iems (my left ear always seems to fit differently than my right for some reason) but it's very rare and only when I'm carelessly shoving them in, not very loud or painful in any way but I've heard that these iems can handle driver flex better than most.