This can mean a couple different things. Your batting is clogged and dirty. You over-filled your cartridge. Your battery is running on low. Your atomizer is not working properly. The first thing I do is change over to a fully charged battery. If that does not solve the problem, I clean my atomizer. If that does not work, I clean my batting and re-fill with fresh e-liquid. Be careful not to over-fill your cartridge. This will ‘flood’ your atomizer. Properly filled, the cartridge will look like a slushy. Really moist with no puddle. If you get a puddle that will not soak in when you use a toothpick to fluff up the batting, you will need to dab the puddle away with a paper towel or cloth. A flooded atomizer will make a gurgling sound when you inhale. It could cause you to draw un-vaped e-liquid into your mouth. Un-vaped e-liquid in small quantities will not harm you but will taste rather nasty.