Without knowing what atty you are using, it's hard to say if you are vaping too high or not. I will assume you are using the stock 2.5 ohm atty. If that's the case, then honestly 4 - 4.3V should be ok. I do work at a B&M Vape shop so I do have some experience with this kind of problem. Generally it's either you have a bad atty or the wrong atty, the atty could be too loose or too tight, or you could just have a bad one. It's a mass-produced product, there is the possibility of a bad one. There is also the possibility that you have got a small amount of liquid in the inner tube, which can cause gurgling and will eventually make it's way into your mouth. In that case, I generally recommend removing the T3S from your battery and blowing thru it, with a towel or something underneath, and then using a swab to clean it afterwards.
My last thought on this issue is not meant to be insulting, but here goes: Are you sure you're filling it right? You aren't getting any liquid in the small metal tube right? I have seen some people think they are supposed to fill it from the top like it's an IClear16 that doesn't have a removable top. Good luck; hope something here helps. I'll check back or maybe somebody else will help you.