Something popped under hood

My car has been making a squeaking sound, I don't drive it a good deal. I took it to the mechanic last week he said nothing wrong. I disagreed. It has been running alright except the noise. Which I thought possibly a bearing. I listen to my engine have had this car since new. I had to drive a ways today. Turned it off then when I turned it on I turned on the A/C after a minute. At that point there was a sort of explosion under hood, steam and I shut it off. No liquid anywhere. Could not find a popped hose or anything visually I could tell immediately. I turned A/C off and restarted it. It sounded fine (squeak gone) checked overflow for radiator watched temperature, oil etc, gauges. Don't know what to think. Don't think my mechanic knows or understands an SS Camaro or my 1996 Tahoe. The Camaro is the only car I have that runs right now. Cannot afford blown engine. Where do I start to look? No check engine light on. No trouble starting could it be the A/C blew and it was Freon. I need a good mechanic here in Phoenix not necessarily a shop that will charge me umpteen bucks for something that costs five to fix. I love this car have had it since new. I am really worried.