On mine the fans will both come on around 50 degrees for a few seconds before shutting off again. I believe this is normal behaviour. They then won't come back on until around 100 degrees
Mines never done it before. I can make the fans come on and go off by holding it on its "fluffy" spot for a few seconds around 2000revs. Most odd. Something has gone tits up somewhere as it's been smooth as anything up to this problem and now it's shit!! Lol