Do you mean these?
xt660-tenere-crashbar
I wouldn't be happy with excess frame vibration. As an experiment I would place the bike on the stand and hold a screw driiver or spanner loosely against various surface parts of the crash rail and rev the bike slowly from tick over to, let's say, 5000 rpm and see where and when the crash bars buzz and make the spanner dance on the bar.
If it vibrates dramatically then my choices would be to remove the bars and clean all the fittings and frame mounts and refit / torque bolts to spec. Or, just check your torque values.
Adding accessories, albeit intended, can accentuate vibration issues. See if removing the lights changes the buzz test. Sometimes adding stuff can dampen down vibration too. Also a crack in a weld on the bars can setbup vibrations.
If it was my problem I know Id be in for a lot of guess work and trial and error.