Hi I’ve just purchased a 2001 V70 petrol.
I test drove it and was fine then drove 20 miles to collect the kid and all was fine.
Five miles into my 60 mile drive home there was a reasonably loud hissing noise appearing to come from behind the dash.
Curiously this stopped when I touched the brake pedal. It’s happened twice more and goes when you touch the brake.
The brakes work fine, there’s no dash lights and the brake fluid level is good with no sign of leaks.
could it be an air leak on the brake bolster system?
thanks
steve

Thank you