I had a similar issue at first. The pin ended up being a little dirty and would stick a bit causing it to go into error immediately at startup because it couldn't drop consistently. I ended up taking the pin out and cleaning it with a bit of alcohol and some high grit sandpaper. It moved smoothly after that.
......or another option (but this might be a bit extreme for you) is to do what I do and use a mains powered bed heater. Then you can use a much smaller, fan less power supply (which of course is totally silent).
