Hyundai Repair: Defrost and cooling, hyundai santa fe, 2003 hyundai santa fe

Question
I have a 2003 Hyundai Santa Fe.  It has 90,000 miles on it and recently I noticed that when I have the air conditioning or defrost on that it makes a hissing noise, almost like a low squeal.  Two days ago, my check engine light came on.  Are these two things related.  Is this something that needs to be taken care of immediately?  Is it an expensive problem to get fixed?

Answer
I cant say what it is for sure with out running a scanner on car to see what codes are there,an as for the hissing sound .there are so many things that can cause I would say take this to a certified tech an see what's going on so sorry I cant tell you more its just one of those things you cant say with hearing or seeing.