Victor 888 "y" cable issues

[theawesome1730]

For our drive train motors we are running 4 CIMs off of 4 Victor 888s using "y" cables to run two in tandem. We keep experiencing a strange issue of one Victor functioning normally when only it is plugged in, but as soon as the second is plugged in the solid light goes dark and makes a high pitched screech. When like that the screeching Victor outputs -12 volts even with no control input. We've swapped them with 884s and they function as expected. Are our Victors bad (we tried 5 out of the 24 888s we have, so it seems very unusual) or are we doing things wrong? We are considering sending them back to Vex and opting for Talons. If you have any ideas please be sure to share. Thank you all in advance