Strange whistling noise from engine

[Matt_Chaps]

Took my 3.4 S for a spin tonight and noticed a whistling coming from the engine, matches revs - higher the revs, higher the pitch…and then whistles all the way back down the Rev range as you’re off the gas. It wasn’t there before when I drove it back from purchase. It sounds like air escaping through a tiny crack but def not AC or vents. Coming from the rear in engine bay. 
 

Anyone had this before on their Cayman? 
 

Any help is much appreciated 

 

Matt

[Andyoz]

Could be a few things. Air Oil Separator possibly. 

[Lennym1984]

Is it actually from the engine bay or could it be alternator whine through the speakers? My first car used to sound like a turbo because of this

[Matt_Chaps]

Only very recently started. It def sounds like it’s coming from behind and is tied to the revs. Barely audible below 2000.

[wtaite01]

Odd question, but has the oil/coolant fill hatch been left open? I noticed similar noises after a service and spoke to my indie about it. I eventually found that this had been left open. I closed it and the noise went away. I was very surprised at the difference it made (as was my indie).

 

Edit - just reread your post, mine was more of a whirring than a whistling, so may not be relevant. 

Edited June 26, 2021 by wtaite01