Was there supposed to be a picture for us to see? If so, it didn't load.
I also get a mean vibration/rattle in my gas pedal at about the same RPM's... but, it's only when I use cruise control, meaning I have my foot off the pedal. It is loud tho, I can hear it over the radio/engine/road noise, and I listen to my music pretty loud. Might try searching on this forum for throttle cable mod, see if the zip ties will help take care of the slack in the line.