If you keep holding up when you beat the level with the wall lifting, the sound of the wall lifting will continue into the next level.
Also, why do you have the ability to duck and slide? This never serves any purpose. I kept adjusting blocks in levels where I could do that to see if there was ever a hole I could slide through but not walk through, and there wasn't. Looks like your hit box is the same whether you're standing or crouching. A lot of platformers will just put in a duck ability and then forget about it without realizing they need to make it affect the game somehow.