Mine will do that if I turn off the fan, it's like a little computer fan.
My tank is at about 80% humidity, my fan broke down once and it was about 95%. I have read various things on the subject but I've not found any sources which say to have below 60% and none that say 100%. Most sources are in the neighborhood of 70-80%. I'd suspect that the higher the humidity the more you would have to watch for mold and fungus problems. To alleviate this you could either add more of a screened top or add a fan.
As suggested, you really need the hygrometer and temp gauge. It's the only real way to know for sure. They are about $5 each, the last thing you would want is to have too high of humidity and have it too cold, then you risk respritory infection.