i've had an Ibanez V70ce Dreadnaught Cutaway for about half a year now. Recently, it's started rattling really bad if i play an open "D." Why? How do I fix this?
my ibanez acoustic did the same thing a while ago. basically the battery box for the electronics was a little loose and i tightened it up a little bit and was good to go! i think the perfect note to set mine off was D also, kind of funny but maybe a D chord or note is one of the more vibrant ones?

if not the electronics then maybe the tuners. you should be able to tell which end of the guitar the noise is coming from.
Warmoth Telecaster Deluxe. Warmoth Strat. Seagull Artist Portrait Acoustic.

"Well good God damn and other such phrases, I haven't heard a beat like this in ages!"
-Dan Le Sac Vs The Scroobius Pip
There's a term for the exact pitch that causes a material to vibrate the most. I remember hearing about someone putting an earthworm on top of a piano, and playing certain notes. When they played a C (maybe c#) the worm started writhing around chaotically. Perhaps the D in question is the Ibanez's (insert word here). This term will come to me the second I post this... well, post.