Open String Buzz

Open string buzz without fretting has to do with the nut being too low. (Check your relief first, but if it was the relief it was buzz in the first 5 frets.)

You can fix this problem with using super glue, accelerator, and baking soda (yes!) You want to apply the accelerator to the D slot on the nut, fill it with baking soda, use something that is close to .035 file. (When I was young, I used knives.) pack in the baking soda, then apply super glue. Wipe off the access, because super glue can cause the nut to melt if it is left on too long. Then file it down to the desired height (Ideally you want to hold the third fret and press down the first fret looking at the distance between the string and the first fret, you want it to be barely touching.)

I hope that helps ask if you need anything else. :)

There's another possibility too. It might be the sympathetic vibration of something else on the guitar. I had an annoying buzz that occurred when was playing up about the 12th fret on the G string. I check all the usual issues and even raised the bridge a bit just in case and it didn't go away. It turned out that the pickguard screw that goes into the side of the body (335 style guitar) was a bit a loose. The pickguard was vibrating in sympathy with the G string.

Before messing with the nut take some time to check for this problem. The fact that holding the headstock makes it go away makes this seem more likely. You could have a friend listen closely around the headstock when you play an open D to see if it comes from a specific place or you might be able to do it yourself since it's an open note. Does the noise also go away if you lightly touch anything on the headstock?

Remember, if all else fails, change the string. Sympathetic buzz can come from a kink in the string.