Yelping noise when he poops

Last 2 days i noticed that my little guy makes a yelping noise that sounds like a stuffed animal squeak when he poops. He also does this odd thing where he stands up on his hind legs or props up his butt as poop is coming out along with the yelping noise. It sounds like as though he is constipated or something is hurting him,



His poop size is inconsistent. Sometimes it'snormal and other times crumbly or sticks together. It's softer than usual yet I wouldn't consider it diarrhea. Other times its somewhat dry, crumbly and small.



He eats a lot of hay and I always hear him running on his wheel throughout the night so his energy level is good. I don't think that it's normal. I felt his abdomen and it doesn't feel like bloat but I gave him simethicone in case.