Jake-Brake

Those are called "Baffles" the unique designs of these baffles redirects the airflow within the pipes to create the sounds. It does not allow the air to flow freely.
Some drivers have been know to even remove them completely.

Kinda like when you hear a car drive by muffler missing or damaged it's loud be cause the air is not flowing properly how it was designed.

 

to be honest I'm not sure what's in a truck muffler but in a car there are just metal chambers that the exhaust bangs off of and that's what makes it quieter I imagine truck mufflers are similar straight pipes dosen't literally straight it just means there is no muffler and that's why they are louder smaller diameter pipes make more of a crackling sound and those really big pipes look cool and make a deeper sound

 

so whats making all that noise is the air flow?? and straight pipes are basically pipes with the bafflers taken out? thanks so much guys

 

I have used mine as a traction check from time to time, just to let know how slick it REALLY WAS, (you know how drivers lie) I'll turn them on medium when traffic is clear, and see if the drivers lock up, if they do, the jakes turn themselves off, I flip the everything to the max off position and continue on my way. used them this afternoon on snow covered road, didn't lock up but turned them down and went on my way. toook me eight hours to go 140 miles but made it in one piece. You need to try what works for you, but wait till you have enough time in the seat to know when to try it. until you do, keep them off if you have ANY DOUBT.