Engine brake question

I have an 08 with 6spd trans. Delete kit, blocked egr., and an edge programmer. My question is why does the engine sound diff. at idle when the brake switch is turned on and off and sometimes it doesn't make any change in sound.? I kinda know how the brake works but I just don't understand how sometimes it makes the exhaust sound different only sometimes. The other night I could switch it on and you could really hear the turbo whistle, and when I switched it off it stopped. I did this back and forth and it changed instantly. It works fine when moving everytime. Just doesn't seem to do anything at idle sometimes. Also I noticed just today that I don't "feel" the turbo at wide open throttle as much. Engine hot and ready. I deleted the factory exhaust BS at 3000 miles and it has only 5100 on it now. I'm using 470 ohm resisters on the three heat temp senser connectors. thanks... Kevin.