Any question answered...

If it's just a loose spoke and you're around east london I'll happily lend you a spoke key or sort it for you. have got red green and black park tools so one should fit.

Thanks chap. I actually live in London, just heading to Norfolk for the weekend. I have a spoke key, but this is my best bike so would rather someone else got it exactly right. I'll have a look and see what I can see.

Have you checked that the brake is accurately centred to the rim, so that both pads touch at the same time? If one side is contacting first, or with more pressure, it could exacerbate any imbalance in the wheel.

Brake is centered, with barely 2mm space on each side. This is essentially a brand new bike which was built up last summer and has seen less than 200 miles. It's this one: http://www.donhoubicycles.com/sparkys-2/