Yea I tend to growl ss well....so much stronger when u make noiseYou could be breathing faster / more shallow due to the stims so the brain has less oxygen and when the valves close you are already lower on oxygen so less time in the valsalva effect brings the darkness more quickly. That or your BP may be going higher already and the valves close ealier due to the already increased pressure.
Getting through the sticking point is when that pressure is going to be the highest. So exhaling after is not going to help. Something that may help you is to growl your way through the sticking point. You are releasing some of the pressure while still retaining the internal / guttural pressure because you need back pressure in the vocal cords to produce a growl. Plus it may make you feel animalistic. I tend to do it on accident when I am really in the zone but I have noticed it releases the pressure and keeps me from yelling out when at maximum effort level in a rep.
Hell for that matter I realize I am growling sometimes as I pace back and forth between a set getting into the zone. My wife pointed it out to me before I even noticed it. LOL I have no idea how long I have done it since I keep my headphones up loud during training.