all guitars were humming except one! now only one is BUZZing, rest are OK, wtf?

Until 2 days ago, everything was fine. But yesterday I plugged in an acoustic guitar to a 312 DI (fabios boards) and got hum.....  so I tried the other channel, same thing.  Tried 2 other channels of my own 312 PCBs, same thing. (mic inputs all work 100%, and DIs all worked 2 days ago).  Then tried a crappy passive DI I have laying around but got the same results (lifting the ground on it helped a bit, but that DI is noisy, I'm not sure...). Even plugged directly to an mbox2pro powered off firewire on a battery-powered macbook and still... huuuuuummmmmmum..  

I also got hum plugging the 312 outputs directly into my monitors as well.

I tried new cables, batteries, 2 other acoustic guitars, and one frameworks guitar.

The frame is the only one that does not hum with ANY of the DIs.  

These acoustics were all working up until recently (well 2 of the 3 for sure, the other I assume was).

I can't think that I changed anything here.  Everything is running off the same wall outlet.  Makes no difference if I unplug the macbook and use only firewire power for the mbox. Still hums. No difference if I touch the jack either. Still only the frameworks "works."

Mic-ins, though, still work 100%.

Can anyone tell me what the heck I'm (not) doing here?

Please help me NOT spend the weekend "fixing" this only to find something stupid (User error) was the problem....

some kind of ground issue on the 1/4 " ?
if common to all pres , you would think the gtr or cable
If common to all gtrs , you think preamp
check the 1/4" switching jacks for making contact & clean them
gtr & cable work o.k. into a gtr or keyboard amp ?
verifing that they work look to what is common to the pres
anything change recently ? , humidity & heat ? power source ?

check ground - faulty cable like ^^^^^^^ said

weird.. just tried the steel string into the amp... no noise (I think, amp is not the greatest).

nylon string acoustic, buzz which mostly goes away if I touch jack and strings. (shielding issue?)

frame guitar, no noise at all.

more weirdness: just plugged into the Fabio312... steel string, no hum. frame no hum.. nylon string, buzzing that goes away if I touch the strings AND jack simultaneously.

my 312s, steel string and frame are OK, nylon string buzzes like crazy..  (same thing going to the instrument input of the mbox).

guess the nylon has to go to the doctor?

used the same cable for all of them and changed batteries on the nylon.


besides that though, why the strange results between last night (original post was from last night, forgot to click "post" and found it today).