Although portable fans can be a convenient way to cool rooms on hot days, they can become annoying if they start to rattle. Rattling is common in a portable fans. As fans draw in air, they also often draw in dust. Eventually that dust causes the blades to become out of balance, which can cause rattling. Rattling can also be caused by a loose front grill. Most of the time, putting an end to the rattling requires little more then a thorough cleaning a little bit of tightening up.
Turn off and unplug your portable fan. Allow the blades to stop turning completely, and if the fan has been on for a long time, allow its motor to cool for a few minutes before you start working.
Remove the front grill from the fan. Box fans often have screws or clips around the outside edges of the grill. Small table fans might have metal u-clips connecting the front front grill to the rear that slide off, and other small table fans might have screws on the rear outside circumference of the fan. All of these can be removed with a screwdriver.
Pull the fan blades off the motor shaft. Most fan blades pull straight off because they install over a slightly raised ridge on the shaft. Others have a small clip either on the front or rear of the blades. Pull the clip off with a pair of needle nose pliers.
Wash the fan blades and the front grill in a sink with liquid dish soap and water. Rinse everything thoroughly, then dry with a hand towel. If possible, place the blades and grill on a towel outside in the sun, which will allow them to dry more quickly.
Take the body of the fan outside, or to an open, well-ventilated area. Spray the motor and rear grill with compressed air to remove built up dust and dirt. The compressed air usually removes most, if not all, of the dust that contributes to fan rattle, and helps get at dust that you wouldn't be able to reach otherwise.
Reassemble the fan by sliding the fan blade assembly over the shaft, and pushing it past the ridge on the shaft to lock it in place. If your fan uses clips to secure the blades, insert the clips until they lock.
Place the front grill back onto the fan and secure it with the original screws or clips. Gently pull on the front grill to ensure that it is on tightly, and adjust it if necessary.