This is the waste gate opening like its designed to do... Option 1, If you want to hear less of this noise you can disconnect the red line that goes to the waste gate and just stick it on an intercooler bolt, this will delay the wg from opening. Option 2, you can pull the wg off of your truck tighten the rod up 7 turns and install a banks big head wg. Option 3, tighten the rod all the way up and forget about it. Option 4, (what I did) ditch the turbo all together and get a turbo off of a 7.3 van engine. It's a bolt on with a non waste gated 1.15 A/R exhaust housing, but you will need to buy an adapter for the exhaust side to use your exhaust. You'll get a bad a** zing sound out of the exhaust when you let off the "gas".
If you decide to do option 2-3 there is a c-clip on the back of the wg if your not careful you'll loose it... I promise you that. What I like to do is take a piece of dental floss, tie it to the c-clip and tie the other end up somewhere else under the hood. This way when you do pop the clip and it goes flying to who knows where you can simply pull the damn thing back to you via dental floss.
Good luck finding your blow off valve