Humming Then Hiss After Turning Off Engine

[AurisVanMan]

Hi. Im new to TOC I normally find answers to my questions by searching old posts but I cant find one on this. I own a 1.4 D4D Auris and have recently noticed that when I turn off the engine it sounds as if something is still spinning, making a humming noise. Then after 5 or so seconds there is a short hiss which sounds like pressure is being released and then the engine goes quiet. I havent noticed this before but only have had the car for 2 months. Is this normal???

[Mooly]

Is it the turbo you hear ? These spin at very high speed and if you suddenly switch off from high revs they will keep spinning for a few seconds. This is one reason why it's vital to idle the engine a short while before switching off to allow the turbo to spin down. Not doing so causes the oil in the bearings to overheat and carbonise and is a major rason for premature failure.

On an Audi I owned I could hear the refridgerant in the air con evaporator "boil off" for a few seconds when switching off giving a "hissing" sound.

[AurisVanMan]

Thats for reply Mooly

I dont think its the turbo as i started the engine from cold yesterday let it idle for about 2 minutes and after switching off the humming was still there.

And I dont have air-con installed in the Auris so it also rules that out.

The hiss I hear sounds like a valve opening to release pressure of some sort. It is a very short hiss, only a second or so. Like the quick burst of air you get when you release the tyre pump off the tyre valve when you fill your tyres. I would like to look under the hood more to locate where it comes from but this irish summer is preventing me from doing so. :-(

[Mooly]

Without actually hearing first hand its hard to say...

Is this the same engine as the Yaris 1.4D4D ? Maybe ask over there :)