Hum In Theta Pro Basic IIIa

I'm keep getting humming sound from my Theta DAC. It is connect to Meridian 518 DSP and Meridian is connected to my old CD-Player. Strange thing is, if I'm twisted the cable connected to RCA out from theta a bit the hum is gone. I got rid of the Meridian once, but still getting Hum sound. I will really appreciate if you guy help me out? Thanks.
Thanks! guys. Problem solved. It was the solder problem. I resoldered the RCA jack. Hum is gone now. Thank you all.
use a power cord and a cheater plug on the theta it should clear up the problem
I would check the soldered connections on your rca plugs to make sure they are tight. The rca "barrel" usually can easily be unscrewed to expose the connections.