It's quite common loved ones make themselves known shortly after death, most people just dismiss it as their imagination, but it does seem an awful lot of spirits feel the need to say one last goodbye and that everything is okay before moving on.
When my father died, he came to my mother and had a long conversation with her, amongst many other private things, he told her how much he loved her and that everything was going to be okay. At the end of the conversation the phone rang, it was the hospital asking my mother to come in, they didn't say so but my mother knew my father had died and of course this was confirmed as soon as she got to the hospital.
The metallic sounding voice I wouldn't worry about, communication by pure spirit is very difficult.
If I were you I would take this whole experience as something of a blessing and move on with your life in the sure knowledge that the love your mother has for you is never ending.