Strange noise from the car tonight--sounded like hissing (MY 02 Turbo.

Driving down the motorway (70 ish just about to take a junction) I could hear a noise from the passenger side like quiet intermittent hissing. Thought it was wind around the passenger mirror or left the window open a very small amount. Checked window but was fully closed.

As it sounded like "static" hissing through the radio I turned it off…...still there about the area of the glove box / vent on the passenger side. Turned off the air con…..still there. No warning lights .

By now Pulled off the motorway onto a roundabout. Hissing on and off around the roundabout and not speed related. Down the A road home and it's still hissing. Sounded like somebody had taken a bottle of coke, just unscrewed the cap a tiny amount and left it fizzing / hissing in the glove box. Eating, drinking etc banned in car so no coke bottle to test theory.

Turned off into side road to house and accelerated to get past junction and it stopped !!

Lifted bonnet at home with engine idling and …nothing. No fluids under car.

Any ideas? Does it sound serious?

Midlife…