I've noticed lately that when I use my vivi nova 2.4ohm on my vmax, after about 3-4 vapes the tip is getting hot. Uncomfortabley hot. I started out at 4.0 volts and have droped down to 3.5 volts with no change. I've changed tips with no difference. I can put another clearo on it and everything is fine. So far it's just that one nova that does this. Any ideas?