Miso soup still has quite a bit of naturally occuring MSG in it. Probably about as much as the ramen packets. Pretty much anything with "hydrolyzed —- protein" listed in the ingredients, or any kind of fermented soy product like soy sauce or Miso will have lots of MSG. The only reason it's not added to the Miso in purified form and listed in the ingredients is because there's already so much in there naturally. It's used to give a savory, meaty flavor (called "umami") to foods.
MSG is just a version of the amino acid Glutamic acid, which is present in most protein. Eating any kind of meat or vegetable protein will result in the release of glutamic acid when the protein is digested. The problem is that eating food with pure MSG added to it results in a flood of glutamate in the bloodstream, which may not be very healthy. But there is considerable debate on whether typical food doses cause high enough concentrations to be harmful. there is evidence both ways.
The truly gross thing in the ramen packets is the amount of sodium. that's probably much worse for you than the MSG.