My son is 2.9 and started covering his ears when he was about 2.5, so it's been going on a few months. At first I thought nothing of it, as it was only if a loud noise startled him eg kitchen blender, noisy plane flying low.
However it's developed and he now seems to do it when he's scared or anticipating something (eg on TV) and more recently if he just doesn't like something or is stropping generally. He still does it in anticipation of loud noises, but there's many loud noises he doesn't bat an eye lid at as they're familiar, eg sirens, Hoover or hair dryer at home, lorries etc. So I don't think it's sounds in particular that bother him.
I've never had any concerns about ASD or any other neuro disorder up until this. His speech is excellent, he communicates with gestures, eye contact etc, plays appropriately (he's obsessed with vehicles and wheels but it doesn't concern me). He's never been upset by changes in routine and has taken potty training, changing nurseries and starting a state play group in his stride with little issues. He does do the ear covering at both nursery and play group, and they say it seems random and not always connected to noise.
Any ideas or experience with this? His 27 month check was fine, no issues, but he hadn't started doing it then so I didn't get the chance to ask the HV. I've seen the GP with him who said there doesn't seem to be anything wrong with his ears.