First, "taking anti-emetics" is not a method to CTB. Anti-emetics are drugs that prevent or treat nausea and vomiting. Therefore, they're really "tools" that some use to thwart the rejection of certain other drugs that a person's body recognizes as poisons and that the body will attempt to expel if introduced into it.
Second...............a "gringo" site? This is an everybody site. Anyone who is on the cusp of wanting to commit suicide, or even anyone who just needs to talk through issues going on in their lives. You can post in Portuguese if you want. Many people will just take your posting written in Portuguese and run it through an online translator and respond accordingly.
CTB with a plastic bag is difficult because of the body's CO2 effect you will have (panic). There could be some "noise" associated with it.
Drowning is what it is. There may be "noise" associated with it. I'd imagine if someone tied weights to their legs and jumped overboard off a boat in deep water, there would be little noise, except for the initial "splash" of hitting the water, since you'd sink to the bottom very quickly if the weights were heavy enough.