Noises from somewhere.

[912.0turbo]

You guys may be able to help me but its kinda hard to describe.I'll do my best. So I'm driving down the highway and decide to drop from 5th to 3rd just to see how my car does. So as soon as I do that and floor it(I have my radio off so I can hear the motor) I hear this small crackling sound and let off the gas immediately. So I wanna hear it again so I go to 4th this time and here the small crackling again and let off. The car pulls good and I was at about 12 psi. The crackling doesnt sound like a rod knock or anything just kinda like when you have a fire going and the wood crackles but real quick. When I go to fifth and let the boost build up to about 14psi it doesnt do it. I guess it only does it at higher rpm. I'm thinking that it may be coming from my transmission but not sure. I have a SPEC stage 2 that grabs wonderfully so far. I hope its not detonating but its a possibility. I have an SAFCII and riched it up a little at the higher rpm but still does it. Its weird because my friend says that when I'm detonating it would sound like a ping or knock. Again its more of a crackling sound.I need an EGT I know but funds are low now. My mods are, Front Mount, walbro 255 ,SAFCII,300zx fuel filter and an HKS EBC. Just wanted to see what you guys thought and pick you brains. Thanks for reading and for your replys. P.S. I forgot, I got off the highway and popped my hood to see if the manifold might be glowing but it wasnt.