The intake comes with two circular machined parts that are just wide enough to fit into the hoses that go to the air pump and another hose next to it.

These two circular cut parts (imagine a metal slug but about a half inch thick with a circular cut, has 3 holes and it says in the instructions that these are "air restrictors" that are supposed to go into the two hoses.

My question is what happens if you don't put these in? or only have one in? Just curious..

I have both in right now.

 

you'll get loud abnoxious noises similar to a cow in labor coming from your intake...:-)

 

Ok I've read this mentioned before. I put them in and it sounds like a cow having labor behind a 5 inch plywood wall. I guess it is supposed to reduce the sound but not completely eliminate it right so you don't feel as though you were in the same room as the said cow.
-Hikaru