Whistle audible at low RPM

[phobia]

Hi all,

This afternoon I have noticed my engine developed a whistle sound noticeable at low RPM 700-1500. As the the revs gets higher the sound is less and less audible, but I think it's still there.

Sounds like a big turbo spool (sadly, it's not that 😭🤣).

When it was colder outside my engine had a whine, a very noticeable one. I was suspecting alternator, bought one to replace it, however the whine disappeared as it got warmer and no symptoms of bad alternator occurred. 

Could this still be the alternator "telling" me it's soon, or a pulley?

 

Regards

[NemesisUK]

Or possibly an air leak in the intake system?

[phobia]

29 minutes ago, NemesisUK said:

Or possibly an air leak in the intake system?

Could be. But wouldn't this throw a CEL on the dash? Or rough idle/engine shaking etc? None of these are present.

[BC99]

Waterpump bearing? Or pulley bearing?