Im getting a hissing noise from my Peugeot 306 convertible, it seems to stop and start at its own leisure!
Any Ideas what it could be?

without seeing the car and hearing the problem for myself l would guess the fuel pump these start and stop at their own leisure. if it does it when you turn your key so your ignition lights come on and stops after a few seconds then it is the pump pressurizing the fuel system and is perfectly normal. hope this helps

Possibly a punctured tyre, check your tyres.

Perhaps an underbonnet airleak - lift the lid and have a listen while someone else blips the throttle