There is a recall for reprogramming the 1.4 cars now.One of the outlined fixes is for a hissing noise from ac after shut down. I also have seen a large influx of bad valve covers causing a chirp noise you would think was a belt noise at idle.It also is in the belt area and is caused by blow by pressure on the crank seal. This has been brought to GMs attention also by our dealer The noise is also loud and can almost sound like a spun bearing at times. hard to believe but true. i have fixed 10 over the last month with a new valve cover.