I actually had the same problem with Vidos and Fengru EMX500, where they would randomly crackle on one side or both when pushed. In my case, this wasn't distortion but inaccurate membrane position, that is, membranes of these earbuds are not glued to the rest of the driver and they are held all around the edge by pressure that casings provide. In my case, if I were to press on them, very hard towards my head, creating additional pressure on the edge of the membrane as a result, crackling disappeared completely. With Vidos, problem went away when I took them apart and put them back together (somehow, on its own, I guess they were not properly assembled, easiest fix ever though). With EMX, it didn't get fixed on its own after reassembling them. I think the best option would be to extend the edge of the rear casing a little so that it pushes on driver more when you connect the front case to it, for now I am thinking of gluing a piece of paper and cutting the paper nicely to the round plastic. (unfortunately, I managed to disconnect one of the cables and have no access to soldering iron at the moment so I can't say exactly if this works)