Last night I decided that it was time to put a decoder in the new AC4400. It runs so quiet on DC that it should just whisper on DCC right? WRONG!! I installed the decoder, placed it on the track and gave it power. I've heard electric can openers that are quieter. I worked on it for a couple of hours to see if I could get it to run quiet, but to no avail. At about 10:00 pm I removed the decoder and rewired the unit for regular DC. I was thinking that maybe it's the decoder that's causing the noise, so I installed it in my Proto 2000 PA1. Expecting to hear a high speed can opener I applied the power and to my surprise the PA eased forward and trundled down the main line with nary a sound. Seems to me that the quiet motors of the RTR Athearn units aren't all they're cracked up to be. I know I won't be buying another one real soon. It's funny. I put a decoder in a cheap BB and it runs without a sound. I put one in an expensive RTR and the neighbors can hear it. Go figure.