Most commonly it's a vacuum leak.
It sounds very much lke you have a leaking vacuum hose. Either it has deteriorated and needs replacing or it has come off its fitting. Carefully check the engine compartment in an effort to locate the source of the hissing sound. When you do repair or replace the hose you will probably cure the source of your idling (and hihssing) problem(s).
You need to put a key in the ignition and turn it.
could be a leaking vacuum hose or missing vacuum system cap
Possibly the compressor has a hole in it. My 2000 Sonata had the similar problem soon within a year of purchasing. The dealership replaced under warranty.
My 2000 v6 had a leaking booster. Brakes seemed fine untill you tried to panic stop, then pedal has rock hard and didnt stop vehicle. Got a used one at a salvage yard, fixed hissing sound and panic breaking problem.
thanks one might be battery or alternatior might be bad
rear wheel bearings are bad
Your valves need adjustment. Take it to your preferred mechanic.
Gladiator won the Oscar for Sound in 2000.
A Sound Education - 2000 was released on: USA: 7 February 2000
Clutch interlock switch may be misaligned or faulty.
U-571 won the Oscar for Sound Editing in 2000.