I have a 2000 LS400 and with about 90k miles. Couple of months ago i started noticing that there is a very high pitched noise when the engine is running. It not very loud from the outside of the car, but it can be heard very faintly inside also. It so high pitched that it’s irritating to the ears. The interesting thing is that when i turn off the engine, you can hear it perfectly for like 3-4 seconds after the engine stops. It sounds like something is decompressing or discharging and the sounds basically ramps down until it no more.

Any ideas on what this noise could be? My first thought is something with the A/C as it has a discharging sounds when the engine turns off. If it was something driven by the engine belt, I would assume the noise would go away immediately after the engine stops like power steering or water pump whining noise (definitely not the whining noise sound like those).

Any thoughts would be appreciated!

 

Bearings are prone to squealing when they are failing. Basically, every pulley driven by the serpentine belt has a bearing in it. There also 2 bearings idling the timing belt.