Side window seals on 2001 Accent

First, be sure the noise is coming from the windows and not the door seals. Often, the top edge of the door sits out and allows air entry. To resolve this issue, bend in the top of the door (unless the rest of the door needs to be adjusted as well, in which case you should start with properly adjusting the door). If the noise is indeed coming from the window weather strip (window run), you may need to replace the window run.

Upon closer inspection, I noticed that the side glass begins to vibrate at higher speeds and separate from the weather strip on the door. At lower speeds the glass is snug against the seal. The door operation seems to be normal.

The window seal (window run) should have a channel in it that prevents the window from vibrating out of it. Most likely, the window run has been deformed.

I solved the problem on mine by adding a tiny line of silicon behind the seal. I was surprised to see the seal was just squeezed there without any glue. I tought it was a mistake (they forget the glue) but a friend had the same noise and also no glue.

I suggest you get the help of another person to reinstall the seal rapidly before the silicon get too hard. It's not that easy to put it back.