I've heard that noise on 2 separate MSC-400s in different homes; one was using standard 418 and the other was an i version. The noise occurred with IR commands and 232 commands, it's a digital noise relating to the antenna (I believe) and is most noticeable while issuing a trigger command during the macro process and volume up/down ramps. Relocating the antenna, using STP, rerouting IR cables, rerouting interconnects and power did not solve it. Putting a CP2e and gateway in solved it :-) I'd love to hear if/how you resolve this, for curiosity sake. FWIW I've never heard this noise with an MRF-300/350, just the MSC.