I have had my 4# pulley installed for about 3 weeks now if not longer, it runs great and no detonation has ever occurred. I just noticed the other day that at idle it is making a noise that wasn't there before. You can't here it in the cab, it's only when your outside, Is this normal or should i be worried. It's not a screeching noise or anything horrible, its just there.

 

You've not given us what the sound is.

But keep in mind it's now spinning faster 100% of the time.

 

No worry
What you are hearing is cavation. Did you notice that big heavy rubber damper on the stock pulley. Go look at your stock pulley and I bet you can figure out why that rubber is in there