[Igofastr]

I haven't had that problem, and I've got 5500+miles on mine. I suspect that you just have some odd harmonics going on. Could be a loose panel, but I doubt it. Have you tried altering the RPM at idle? Does it get better? As a last resort, after checking to make sure it isn't actually loose, you might want to try sticking some of those "sound deadening" sheets to the panel (I'd do it from the trunk side)...can't think of the trade name at the moment, but it may alter the frequency of the panel enough to prevent the vibration.

Good luck.