Installing a Eclipse CD4000 unit. I am using the factory speakers and amp. I have a harness from metraonline.com. The harness plugs into the factory harness (that the radio used to) and accepts the RCA inputs from the headunit. Once I plugged the headunit into the RCA of the the harness, everything worked. However, the buzzing started once I powered on the headunit. To troubleshoot, I disconnected the RCAs from the headunit and just ran speaker wire/speaker to one of the speaker wire sets on the headunit. The buzz was gone so I knew the amp caused it. Called Metraonline and inquired and they suggested the RCA groundloop isolators. The isolators get connected inbetween the headunit and the metra harness. This help?