It sounds as though you might need to get it looked over. Sometimes the seam can be coming open, not so much that you'd notice it, but enough for a luthier to spot that it was. It might be aggravated more by different temperatures in different rooms....Hence magically disappearing when in a different climate.
Sometimes you can work out what it going on yourself.- Bow your cello while holding on to the seam bit by bit all the way around. It can be tricky - especially if you're not a natural contortionist
Also grip the endpin while you bow, then the tailpiece, and each adjuster in turn. In fact try every part of the cello you can - clamping down with one hand while bowing with the other. It might just be a set up problem.
Best to get it checked over when you can though.