I'm currently having the same problem. The ac repairman diagnosed the problem with my nest thermostat on Friday and will be back on Monday with the replacement parts. Well, I originally was having problems with my unit making low train horn like noises when turning on and then after running for a couple of hours the unit makes an alarming noise and sounds like the unit may blow up. The first-time I had no idea the noise was actually coming from my house and it sounds like a car or 4 wheeler engine in need of help. Well since Friday this noise much more frequent and the furnace continues to short cycle, but after 30 seconds or if I'm lucky 4/5 minutes, then the most startling 'RAAWRRRRr' bellows from the unit and sadly 'the ac game' is over. I immediately raise the temperature, wait a few minutes, and eventually lower the temperature a degree or two. Currently at 78 in Louisiana and looking forward to Monday. I love the convenience of the nest but I love having a working ac unit more.
