so I bought this new mixer (http://www.musicstore.com/en_EN/EUR/Fame-MIX-1604FX-PRO-16-channel-mixer-DSP-effects/art-PAH0009261-000) and the behringer UCA222 interface, which are connected by RCA/RCA, and most of the times (yes, it doesn't happen always) whenever I'm listening the drums through...