I have a 2008 S-Type 4.2L (not R). There is a "buzz saw" noise coming from the engine bay. Its only noticeable when idling (in gear or not). When I activate any accessory the engine idle increases (like turning on the air conditioner) the noise goes away due to the increased RPMs, but immediately returns once the engine idle returns to normal. Turning the steering wheel has the same results. Anything that increases the RPMs makes the noise go away until it returns to normal idle. Other than this noise, the engine is running perfectly!

 

Welcome to the forum.

To isolate the noise, try removing the serpentine belt and running the engine briefly. See if the noise ceases. If so, you'd know the noise is coming from one of the belt-driven components. Only run for a minute or two like this, as there will be no coolant circulation with the belt removed, and you certainly don't want to overheat the engine.

With the belt removed and engine off, try turning each accessory pulley by hand. Maybe you will feel some roughness or binding, indicating a bad bearing or similar.

If still no help, reinstall the belt and get yourself a Steelman EngineEAR:

https://steelmantools.com/products/e...ar-stethoscope

The microphone is highly directional and will pinpoint the source of the noise. I have one of these puppies and it is amazing for chasing noises. For example, I was able to find an AC refrigerant leak that defied all other leak testing methods. I could actually hear the otherwise imperceptible hiss from the refrigerant leak.

Steelman offers two versions of headsets. I recommend the larger earmuff style over the smaller Walkman version. The large cups helps block ambient noise.