My son used to do this when he was younger to hand dryers, hairdryer and various other noises that he may have thought were too loud. He stopped for a good few months and I thought he's grown out of it etc. Yesterday he started again at playgroup and he's done it again this morning watching tv. It was suggested by HV that it is an autism trait however I've looked into the other signs and it appears that he only has this trait. Ears were checked at hospital a couple of months ago and showed he has perfect hearing. Anyone else's children do this? Did they just stop and start? Any info appreciated, thanks