In most cases, a noisy filter is caused by air lock-ins. These are air bubbles in the rotor housing, causing vibration and scraping of the rotor / impeller against plastic.

Prolonged running of a filter like that can cause damage to the rotor / impeller.

How to remove the air:

1.) Unplug filter (never run a filter without water - this will damage the unit!)

2.) Take filter out and shake it a few times

3.) Submerge the filter again and give it a few shakes underwater

4.) Plug filter back in 

5.) Give it a few shakes and knocks to knock out any trapped air

This usually solves a majority of noise complaints with internal filters. Should the unit still be loud, have a closer look at the suction or installation mechanism and make sure the filter housing is not touching any glass or decoration. Vibrations (noise) will be transmitted and increased that way.