whistling sound when engine is revving

Hi,

Whistle noises could be normal however, the way you describe this one it sounds like an air leak in one of you intake tubes.

Here is a guide that goes through some common noises but again, I don't think this your issue but it does give good ideas on how to address these:

https://www.2carpros.com/articles/car-whistling-noise

I would suggest inspecting the intake hose very closely. You can spray some brake clean or starter fluid on it as well and see if the RPM's go up. If it does this means you have a leak. Basically this is how you find a vacuum leak and this is basically the same thing. The only difference is, this would not be considered unmetered air because it is probably not after you MAF sensor.

Let me know if you have questions. Thanks