hissing noise on clutch pedal release

'90 wrangler. rebuilt ax15 tranny and new clutch installed, as well as a new clutch pedal (long story) (less than10miles ago). clutch engages successfully but as soon as I let up the pressure on the pedal there is a hissing noise. the slower I release the clutch pedal the more pronounced the sound. sounds sort of like air escaping.
anybody have an idea???
thanks in advance.
also I just failed the NOx part of my NYS inspection. test limit 2.50gpm - vehicle reading 2.90gpm. Mechanic said my coolant system needs to be flushed and a new thermostat installed to correct the readings. additional thought????

[RRich]

The noise - Hissing is while the clutch is still slipping or after it's hooked up?
If when slipping, probably it's just breaking in -- worry after 100 miles and it still makes the noise.

NOx - overheating can drive NOx up. Also over advanced timing, too retarded timing, too lean a mixture, not enough EGR, carbon in the chamber, etc.
Anything that drives the combustion temps up. Oxides of Nitrogen form when the combution temperature goes over a magic number just under 3000 degrees.
If it's running extremely hot, then he's on the right track.

[Olin18]

The hissing noise could very well be ether air in the hydro clutch system. Did you bleed the clutch really well after it was in. Wouldn't hurt to do it again.
It could also be the sound of Hydro fluid leaking out of the system somewhere. Check all the connections to make srue there are no leaks. IF there are just tighten them up.

Trying to make a long story short. The NYS DMV ordered this mechanic to install an off the shelf rebuilt ax-15 and a whole new clutch assembly (including a clutch pedal - he cut down and re-welded the old one to make the first incorrect clutch he installed work). he destroyed my tranny as well.
The Important part - The mechanic let this car sit around from Sept to Late Feb. I had to let it sit from Feb till a week ago until he was ordered to fix it. QUESTION: could the cold winter in NY have affected the results of the inspection??? The job was only completed 7 miles ago. The car was only moved maybe 50 miles (part by tow truck) since September.

[RRich]

Something sure doesn't sound right -- the NY DMV ordered a new trans and clutch? They must have owned it.
The trans has absolutely NOTHING to do with emissions.

sorry for the confusion. I got the NYS DMV involved because I got nowhere with the mechanic. They stepped in and made him correct all his mistakes. My jeep sat idle prety much from early Sept through the entire winter until a week ago when they lowered the boom on him. He kept my car from me (it's a long story) I just got my vehicle back 4/27, brought it to a different shop 4/29 where it failed emission inspection. I wanted to know if the car sitting idle for almost 8 months caused the NOx emission failure. If so I want to go after him for that too. This mechanic was a real lying piece of garbage. he banged me out for $3000.

[RRich]

Oh, I remember the problem you had - You'd told the story. But I had no idea it was the DMV that would be the authority. The clutch pedal shortening reminded me. Good that they stepped on his neck!

Our DMV doesn't do anything except charge money for everything.

Sitting shouldn't affect emissions, unless possibly the gas is old. Gas addatives only last about 3 weeks.
Anything that causes combustion temperature to go up raises NOx. Timing, retarded or advanced, overheating, lack of EGR, etc.