I bought a Marantz CD5400 from SuperFi.co.uk to replace my ancient Philips cd player. When I installed it I found that there was an annoying hum coming from the box. This noise was easily audible from 1 metre away.This was present even when I disconnected it from the rest of my system. It stopped if I put it into Standby. I informed Super-Fi and they arranged to pick it up and sent out a replacement, however the replacement hums exactly the same. I've tried it in various sockets in my house with the same effect. When I talked to the SuperFi support person he said that he had my returned unit but could not detect a hum unless he placed his ear against the case and that this was acceptable and therefor the cd player was performing to spec. He suggested it might be caused by my house mains supply, however none of my other equipment hums. Also, this guy was clearly in a warehouse because I could hear what sounded like fork lift trucks and creaky metal doors in the background so hardly a fair test. They agreed to take the cd player back and refund me but only if I paid the cost of posting it. I'm loathe to pay £10 just for the pleasure of reviewing this cd player. It was awarded 5 stars by What HiFi in 2003 but I reckon Marantz must have down graded the power supply spec since then. Has anyone ever heard of this problem before, and how could I eliminate my house mains supply as a possibe cause of the problem?