A few months ago I put a complete (used) banks turbo kit on my truck. For the first 200 miles or so everything was going great, but then about 50 miles into a trip with the truck loaded with a cabover camper I began to notice a slight whine while on the freeway ( constant boost of about 5-6), which progressively got louder. I now hear it every time I get the boost above 5-6 lbs, and it gets louder/higher pitched as boost increases. It doesn't make the noise if I rev the engine in neutral, but if in gear and I keep my foot on the break it will start up when the boost gets high enough, even at a standstill.
I got a rebuild kit and replaced the bushings, o rings, heat shield, etc (everything that came with the kit), but the sound is the same as before.
I recorded a video this morning, but don't know to post it.

Any ideas? Thanks.

 

Upload the video to youtube, photobucket, wherever, and post the link here.

 

sounds like you have a boost leak.

 

I pulled the hat off last night and the o-ring is missing. That could well cause the boost leak and high pitched sound. I'll pick up a new I-ring and see if that improves it.

Thanks!