Port noise sounds like extra air coming from the box.
Think of a bycicle pump. You know that sound of compressed air? Well its like that but on a much smaller scale.
Speakers are compressors after all. They move in and out like a piston to move air to create sound.
When the port is too small in length or diameter it makes that noise. So to remediate the problem just go up one size on the diameter of the port (the length will also change).
If the speaker sounds like it pops or has a snap ring to it; it may not be port noise. It may be over driven (too much bass boost or too much volume). It may be that it is bottoming out (X-max). It may also be that you hear a tinsel lead (wire that is connected from the speaker terminal to the voice coil) slap.