HI, I have a 1988 chevy pu with 110k on it. I starts right up and drives fine but after it gets warm I have a hissing noise that comes from the exhuast and a pan sounding knock only when not under lond at low rpms any body know what this is.

Thanks for you help  

The hissing noise could be a bad exhaust manifold gasket or the exhaust doughnut.

The knocking noise, that's a tough one. How's the oil pressure when the engine warms up? What weight oil are you running?  

hey guy, sounds like you have a stopped up catalytic converter. it's located under pass floorboard, you can have a back pressure test to see if this is the problem. the pancake style was prone to do this. the replacement converter will be a straight through type witch is a lot better.

Thanks
Lee  

Oil pressure is about 30-35

Thanks  

Thanks Lee I was wondering if it could be the cat...