I have a 06 lbz duramax with aftermarket boost tube and egr blocker and when I get up to 15 psi of boost it give a burst of air sounds like a blow off valve . I kno they don't have a wastegate so not sure what is goin on please help

 

i would check intercooler boots.

 

Make sure your egr plate is sealed all around it. If there not sealed properly they have a loud air noise coming out of them