Oh, no, I'm not using one of thems.  And I have the same issue on my PA's inputs, and they have no effects input.

no an insert jack is sometimes on a mixer. it is used for effects and stuff but if you plug a dmg it could cause the problem you are talking about.

do you mean a wall jack?  Because no.

is on plugged into an insert jack? that would do it i think.

Cool thing though is that when I plug my gbc into the link cable it seems to ground to the dmg, effectivley stopping any extra buzz that the color would normally have.

Hmm... this just gave me the idea of an optoisolating link cable, or maybe even just a module to go between a Game Boy and the cable. I can't imagine many people using them though. I've never heard of Game Boys having ground loop issues while syncing before.

works no problem without link cable...

yea that is odd.....have you tried the two gameboys without the link cable?

because when fuxxing with a cable for nano 2.1 to lsdj sync i once experienced the GBAs audio being cut by the link cable being improperly grounded....but thats nanoloop.....

That's what I figured.  But I have no idea where it's going wrong...

maybe one of these bastards?

http://en.wikipedia.org/wiki/Ground_loop_(electricity)

So I have two prosound DMGs with two copies of LSDJ linked together master/slave.  My PA has two inputs, so I plug both the DMGs in.  However I can only hear the first one.  I played with the volume on the PA, but got nothing out of gameboy2.  They both say they are playing.  But it gets weird because when i unplug the jack from gameboy1 then suddenly gameboy2 is able to play.  And as soon as I plug gameboy1 back in I can't hear gameboy2.  This same problem persisted when I tried it on my mixer.  and when I used a y-cable to combine them.  But the same setup works if I replace the 2nd DMG with my color...

What the hell?