If it is a squeal, I would think of belt making it. Any condensation water dripping on belt or pulley?

 

It's after the engine is turned off, can't be a belt.

 

Air conditioning have hissing sound, sometimes when engine is turned off. That is gas passing through air conditioning pipes and evaporator.

 

That's what my dad suggested. Is it something to be concerned about?

 

I'd say it's the aircon gas just exiting or moving around the pipe.


The system is under some major pressure when in use, then you've turned it off....

 

You sure it isn't from the stepper motor on the throttle body? - it is normal for this to emit a high pitched 'whine' for a couple of minutes after the engine is switched off.

 

Why on earth would it do that? Is it still spinning or something? Not that I'm doubting you, cars have to try really hard to surprise me these days. Any way of diagnosing and fixing if it is?

 

Below the coolant tank is a part of the aircon system known as the thermostatic expansion valve and it can make a hissing sound after the aircon system and engine have been switched off due to the still under pressure refrigerant passing through it.

If this is the source of the noise it is nothing to worry about.

 

The aircon seems to be the best bet because it didn't do it today after getting home without using the aircon because our stupid weather has the yips at the moment.

Oh joy, my MG makes weird noises even when it's just sitting there.

 

She's stopped doing it now. I can only assume that I've been given the correct advice and that now the noise has been 'outed', it's had to go underground for a bit.