After picking up a ThinkPad X250 I paired it with a dock. The dock was an engineering sample. Cheap, but with its share of problems. Most of them I can live with — no triple-monitor output, for instance, which I don’t need anyway. The real killer is that when the machine isn’t plugged into power, external audio picks up a loud hum. People reported this on the official site and on Youtube. It turned out to be a hardware fault on Lenovo’s end, and only got fixed after Lenovo recalled the thing. Like I said, though, mine is a cheap engineering sample, so no recall for me. That doesn’t mean there’s no fix. Just get an external sound card…