Power Converter Buzzing

I have a DC to AC adapter that I use in the car. I have used it with no problems with a variety of electric devices. However, when I use it with my laptop cord, the power converter brick buzzes. I did some research, and some people said that buzzing happens because it uses a "modified sine wave" rather than a "pure sine wave."

The reason I'm worried is that when power supplies or chargers have gone out on me, they make this buzzing noise right before they die. Should I be worried? Is it worth investing in a special DC cord for my computer?