welcome, Kaleun
in stock, going to 'silent running' is not enough
take a look at your rpm, if it is above 100 (or even 50) one of those boys who is sitting still above you can hear you, then they might go pinging for a while to nail you down
in gwx, rpm drops to 99 or so at silent running. 50 or even 0 is still better
manually set to 50 by ordering a speed of .9 knots, or simply cut the engines
you can check the rpm best from the view in the conning tower. if you didn't get that, please say so i'll try to explain more clearly