[font=trebuchet ms]Fret buzz is the sound made by the string slapping a fret as it vibrates. That will definitely go through the amp, because the string is buzzing.

If something else is loose, it may rattle when certain notes are played. That might not be heard through the amp if the string(s) aren't affected. Check all of the hardware. If the knobs on the tuners have a screw to hold them on to the shaft, that is a prime suspect.[/font]