Under boost, my turbo has been making noise similar to a sports whistle, not the usual "whirr" sound. It's very loud in the cab. Can't tell if it's the turbo, waste gate leaking, or possibly a cracked intercooler? (it's plastic). I replaced all the boots with silicone. Any thoughts? Thanks.

 

Help!

 

Sounds like a leak. I had a loose boot do the same thing..
May want to pressure test using compressed air. There are some examples of creating this with PVC parts from Home Depot on the site if you search around the site.
Putting the air pressure into the system will help find the source of the leak.

Good Luck

 

Does the niose get louder when you hit about 5psi of boost? If so then yes you have a leak or small hole in one of the boots. It's only going to get worse until you blow it out or off completely. I know been there done that. Make sure all your clamps are far enough back and holding correctly, alittle soapy water can help somtimes in finding the leaks.

 

I would check all of your intercooler boots. I recently replaced all of my intercooler boots. The boot off of the turbo was in bad shape and appeared to be coming apart with strings of material hanging off of it.