Why does my car shake when its on drive?

And reverse but not when its on park or neutral but when I'm at a stop only, the vibrating goes away when I drive, and when i turn on the AC the vibrating gets worse. Which results in a really loud vibrating with the AC on, I've took it to some mechanics and they don't really know the problem its a 2005 Honda accord lx

Its what we call… Missing. Have a shop run a diagnostic on it. Won't be much unless you decide to have them fix it, but do it soon.