Just had my engine rebuilt with brand new everything then went with a used, good condition A-Spec single turbo kit.

There's a weird fluttering sound, only at idle, that sounds almost like air is hitting a piece of paper. I can't really pin point where it's coming from. When I rev to about 3k RPM it goes away, but comes back whenever I'm sitting. It sounds like it's coming from right below my shifter.

I bought a used, low mileage single turbo kit with used low mileage injectors. Could the injectors be making noise at idle if they're in bad? Could that be the issue? Could it be the engine seals? Vacuum leak? Or maybe it's something else? Just an annoying sound I want to get rid of...

 

Could be just the turbo noise. Post video?

 

I'll post a video when I get a chance but I highly doubt it's the turbo....

 

Did your builder use a new LIM gasket? The metal one? I reused my old one and had that sound and also what sounded like a balloon squealing when you pinch it and let the air out but I only got that sound under boost. Put in a new LIM gasket and guess what? Sound went away. I heard that flutter sound through my intakes at idle. It's gone now.

 

I'm thinking exhaust leak.

 

Just found out it was two bad injectors (2200cc). Even though they were flow tested and cleaned it was only pumping out 1200cc. It was rattling / vibrating the pump lines which then made the weird fluttering sound. I think stepping up to nylon braided lines will also further eliminate noises. Hopefully this will help anyone else in the future.

 

I'm just glad you came back to update us on what the solution was.
So many times people will make a thread trying to diagnose and fix something, and you never find out what the cause was or how it was fixed because OP never comes back.