Engine is making hissing sound.

It could be air in the power steering system. Check the power steering reservoir to ensure it is properly serviced. If it is, check for any evidence of leaking under the car - power steering fluid is usually either clear or reddish color.
If you have to add fluid to get the reservoir back up to the correct level, it will take a little while to get air out of the system, so the hissing may continue for a period of time.

It can be a grinding or whining noise. you may also feel it In the floor or steering wheel

worn out steering rack, or box and rag joint .

it can be a number of things ac clutch idler pulley trencher alternator power steering water pump and belt most likely is an old belt because its stiff and slips when cold it warms up the belt is more flexible and it grabs beater the trencher can be weak and with the cold belt it can slip

need to check for engine codes. sounds as if the exhaust cam actuator is stuck open creating an internal vacuum leak. the actuator is on the right side of the engine behind the power steering pump on a 4.2 liter engine.

Sounds like you may have low power steering fluid.

CHECK COOLANT LEVEL SOUND LIKE COOLANT LEVEL GOT TOO LOW IN WHICH ENGINE WILL MAKE A TAPPING NOISE ENGINE GET TO HOT IT WILL STALL OUT.

Check and see if you truck is getting to hot. this sounds like dieseling caused by overheating. the hiss is just part of that

check the idler/tensioner pully's and the alternator pully, there is a common problem with one of these 3 going bad, usually an idler pully the best way to check is to get a mechanics stethescope and touch the end to the bolt on the idler pully's you will notice a very distinct sound difference from a smooth pully and one with bad bearings. gm tech here, seen many of these

Check Power-steering Fluid level and make sure that fluid is good first. If Fluid is good and when you accelerate the vehicle its fine then, you need a POWER STEERING PUMP. Good Luck and thanks for using FIX YA