It's faint, but whenever I plug my phone into the charger, the charger makes this high pitched buzzing/whistling noise. I checked with multiple outlets and it does it for each one. Is this normal and/or safe? I just don't want the charger not be fully charging my battery, and have my overall battery life be affected, and I want to know if it's a safety issue. Has this happened with anyone else? It's always done this too.