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Need some help with a noise

Looking for some friendly direction on a noise under the hood. I’ve got a 2004 SRT-4. The car starts, runs, and drives great. But, when I let off the gas I get a high pitch whistle that starts around 2200 rpm and stops around 1900 rpms. I’ve sprayed water on the wastegate, vacuum lines, and intake manifold, but not seeing any of it being sucked in or bubble. Thought maybe a pulley, but there’s no wear or fray on the belt that would suggest that would causing it. Any help would be greatly appreciated.

Let’s be clear on what the whistle sounds like. Is it a steady, decreasing in pitch tone, or does it sound more like this:

If it’s the latter, that’s flutter, and it means your blowoff valve isn’t opening as it should, and backpressure is hitting the turbo vanes rather than being vented.

If it’s the former, I’d be looking at the surge valve - it routes overpressure back to the intake, and if it sticks open slightly internally you can get a whistle without ever seeing any signs of a leak on the outside.

Is it possible it is coming though the sound system? My car on am radio between 580 and 720 am gives a high pitched tone that decreases in pitch when stopped at a light

It does sort of sound like a turbo problem, but another idea, when you let off the gas and coast the vacuum in the intake manifold increases. If you have a tiny air leak into that space it could create a whistling sound. I had a car years ago with a tiny air leak in the valve cover gasket, and when the engine was running the inside of the valve cover was under partial vacuum. It would whistle like crazy when ever the engine was hot and idling or at slow speed, like in parking lots. I mean a really really loud whistle, like a coach would use to bring the team to att’n. I was able to fix that just by re-torqueing the valve cover bolts.

Sorry for not replying quicker. It’s definitely not turbo flutter. After you mentioned intake did a little more looking and think that’s where it’s coming from. Really appreciate the help.