Never had this happen before

ok this is a new one for me yesterday did a brew 2 5 gal batchs everything went good I of the batchs when I looked this morning is bubbling away doing great. the wheat beer batch I did is sucking air in thur the bubblernot blowing it out? Never seen this before any help?

The fermentor that is sucking air might be cooling, causing a drop in pressure inside the carboy.