PTAC makes long Gurgling noise?

[spedprof]

Folks,

I have a PTAC unit in my bedroom in the Long Island, NY area. It's about 6 years old. I know that there is a kinda gurgling noise that is common to PTACs that is ok, but this one seems to last for a minute or more and is then followed by a hissing sound like a gas is released. Does this sound normal, especially the length of the noise. Is it a sign that needs and can be repaired or is it a sign that it will need to be replaced soon. Once during the summer a similar but different noise got louder and louder until I had to turn the unit off for fear that it would explode.

Thanks in adavance. Merry Christmas!!