I notice this morning that my 2009 Nissan Maxima has a high pitch ringing coming from the engine area after the engine is turned off. Not sure if it's a bad sensor. I have no fault codes or check engine light issues. The car is garage and has 183,000 miles. Just had new tires installed, replaced both lower control Arms, both front drive axles, both rear springs and new rear sway bar linkages along with an alignment.

The high pitch is just like tinnitus, the ringing is continuous after not running for >24 hrs

 

Without a recording I can only guess.

Maybe a small hole in hose or radiator?

A bearing in your electric fan?

Vaccum leak (booster cyli

Your car has developed tinnutis?

 

Have you replaced the radiator filler neck yet in 183k miles of driving? I have a 2010 and when I started smelling coolant every now and then I found that my lower radiator hose was leaking, and my radiator filler neck had a small crack in it that only leaked fluid when the car got up to temperature.
I heard a noise similar to what you described after a long drive this past July after I parked in my garage and had to come back to my car to get something. In my case, the noise only occurred when the car was hot, and it only lasted for about 15 or so minutes until the pressure was released or the car had cooled down some. I eventually changed the lower radiator hose and the filler neck.

 

The newbie gave nothing to go on

video clip would be nice!

 

But he said "tinnitus" !! He gets points for that!