Brand new Lowden F-25 has light metallic sound when played open or fretted (B string)
 

I recently purchased a new Lowden F-25 and am having an issue with the B string.

I play almost exclusively in DADGAD, so I had the truss rod adjusted slightly to help reduce fret buzz. Since that change, the B string has had a light metallic rattle when played open or fretted when I attack fairly hard. This happens in DADGAD or standard tuning.

Does anyone have an idea what could be going on?

Sounds like it's just barely hitting a fret somewhere. Is the break at the saddle a bit low, or is there a fret somewhere that's sitting a bit high just under the B string? How low is your action?

I'd be surprised if it is hitting a fret. This is a new phenomenon since the truss rod was adjusted to raise the action. Unfortunately, I don't have my guitar at the moment so I can't check for high frets.

If I listen closely enough, it sounds like the noise is coming from the saddle area. However, I've read elsewhere that that could be a red herring.

There you have it: the truss rod is not for adjusting the action.

The rattle can come from poorly seated ballends.