jtwags

As the Texas summer sets in I have been using the A/C more. The other day I heard a very strange noise coming from what sounds like the A/C system. If I shut the car down and run into a store for a few minutes and then start the car back up in a short period of time, say 5-10 minutes, I hear a strange sound that resembles the sucking through a straw like instrument (hard to describe but starts like a low whistle then ends with a high pitch whooooop for a moment). I am thinking it may be the expansion valve but not sure. Has anyone experienced any strange noises like this before? Only happens when car has been run for a while with the A/C on and then shut down for a few minutes before starting again, maybe some kind of equalization noise??? A/C cools just fine, no noise from compressor either. Thoughts?