#1
Last night I was tuning my low E down to a D and whenever I played it, something near the bottom rattled.
Is this a bad thing?
What might it be?
I'm aware we're in a church.
Yes, my daddy's the minster.
I know he's preaching, he does that every sunday.
Oh, what are these?
Tarot cards of course.
#2
it sounds like fret buzz. its not a bad thing, it just makes some notes unclear and its annoying.
The Gear:

Custom Strat
Mesa Boogie Stiletto Ace
Fulltone OCD
Electro Harmonix Small Clone Chorus
Dunlop Crybaby Classic
MXR EVH-117 Flanger
Fulltone Soul Bender
#3
Fret Buzz - when you switch to dropped tunings, light gauge strings will most likely buzz the frets when action is set low.
Schecter C-1 Classic (Antique Amber)
Ibanez JEM 7VWH
Crate Palamino Class A tube combo
Digitech RP80 Multieffects pedal
Ibanez TS9 DX Tube Screamer
#4
bottom???? do you think you could be a bit more specific. but like said it probably is fret buzz