KEF 107 KUBE buzzing sound

I'm noticing a fairly significant buzzing sound that appears to be coming from my KEF 107 KUBE. When I remove it from between the preamp and power amps, there is no buzz. I didn't notice this before when running with an older McIntosh MC752 amplifier, but I definitely hear it with both my Emotiva XPA-1L G2 monoblocks and my Odyssey Stratos Extreme monoblocks. I'm thinking I may not have noticed it in the past due to the lower input sensitivity setting on the McIntosh. Any ideas? Could this be caused by leaky caps? It doesn't sound like a 60HZ hum so I doubt it's a grounding issue. Any suggestions would be most welcome! :)