A bathroom is usually a small enclosed room which is often full of moisture laden air. The conditions are ideal for moisture damage and mold growth. This is why it is so important to have a properly working ceiling fan in your bathroom. Some might feel like the fan is just an unnecessary noisemaker in the bathroom, but you should always have the fan running when taking showers to funnel all that moist air out of your bathroom.
Just having a fan installed is not enough. For the fan to work properly, it needs to have a duct leading to the outside that is as straight as possible. A fan that is venting to a location inside your home is just moving that moisture laden air to another area where it might do damage undetected. If your fan makes a lot of noise it could mean that it is about to fail. You should replace it with a new fan as soon as possible.