I have the same problem too, it always happened when the clutching of compressor is too rapid especially during raining day. What I did normally is to set the temp. a bit higher. I was told by 'insider' that it is something to do with the compressor which is an item that was not assemble in Korea. Maybe you can verify this during workshop clinic conducted by Korean 'specialist' in S'pore, which I did but I had a lot of argument than problem solving.
Most carens owners here complain over cricket noises thru air conditioner duct... blowers start squeaking after 2~3 years, and no way to fix unless you replace the whole blower. I think a little hissing noise from the compressor should be the least of your worries.
I agree with you guys. May be mine is even worst. During rainy day, the AC will blow off bad smell. I've serviced it twice but the smell still exist. Another thing, I noticed my Caren AC compressor never stops from the moment I switched the AC ON till I switched it OFF. I've tried replacing the duct sensor. Nothing happen. Right now I'm still looking for ways to modifying the AC circuitry? Any clue?