My son used to do the same thing beginning around age 1 and up until about age 5. He will still do it occasionally but now he is able to verbalize when something is too loud and bothering his ears. Is this the only sign your child is exhibiting or are there other symptoms/signs of autism being exhibited? My son is not autistic, he just has sensitive ears.
As for the potty training, every child is different and will learn at their own pace for whatever reason? My daughter was potty trained at age 2 with very little incident. My son was practically 5 years old before we got him trained completely. What I finally had to do was put him on a schedule so to speak. Basically, I would wake him up at the same time every morning and immediately take him to the bathroom. Varying his wake up time by more than an hour can be disastrous in the way of an accident. Then I would send him or take him to the bathroom every hour after that to see if he could go potty. Even if he argued that he didn’t have to go I would make him go try anyway, and he argued a lot but amazingly almost always went potty. And I always made him go potty right before bed time. It is very important to be vigilant about this schedule. Also, I know that this can be very frustrating and it’s difficult not to get angry when accidents occur but don’t. Resist the urge to show anger or displeasure when he does have an accident. This was a source of shame for my son to the point that he would try to hide his wet pants from us and would cry when we discovered them. Getting angry and yelling will only cause anxiety for everyone especially your child and will not help resolve the problem. This will most likely make it worse. When accidents do occur, just tell him it is okay that accidents happen and we’ll just try harder next time. You need to provide a lot of encouragement and a lot of verbal positive praise when he does potty each time.
Also, our pediatrician advised us not to provide too many beverages containing sugars like Kool-Aid, juice, soda or Gatorade after 7p.m. as the sugar encourages frequent urination. She advised that water was to be given after 7 p.m. and even then to limit the quantity. I purchased the small 4 oz sized disposable drinking cups (H.E.B. has a brand that is very inexpensive) and limited his intake to one of these cups right before bedtime.
My son is also a very heavy sleeper and wouldn’t wake up when he got the urge to potty at night. What I discovered was that my son would whimper several times at night and I thought he was just having a bad dream. Those whimpers were actually my queue that he needed to potty. Whenever I heard him whimper I would wake him up as much as possible and run him to the bathroom to potty and then tuck him back in bed. You can accomplish this with a baby monitor as long as you wake up when you hear him and take him to the bathroom. Also, my son cried if we put him in pull ups because he said they were baby diapers. So I went out and bought several of those flat (not fitted) flannel/vinyl crib mattress pads. I sewed extra fabric on the top and bottom ends and then laid the mattress pads on top of the sheets width wise and used the extra fabric to tuck under the mattress to keep it in place. That way when there was an accident I didn’t have to change the entire bed and bed sheets in the middle of the night, just pull off the crib mattress cover and put a new one on.
All of this will take a lot of time and patience and there will still be some accidents along the way but they should get far and few between the longer you stick to the schedule. It is very important to keep the schedule and make him try even though he insists he doesn’t have to go potty. Make him go in and pull down his pants and try anyway even if you have to go in and stand by him at the beginning to make sure he really does try. Eventually it will catch on. I hope this works out for you and good luck!