A Brompton has recently come into my possession on loan. I was charged a very modest amount by The Cycle Service to get it working again and all is good. It does have a wee rattle I cannot figure out and I found a small piece of white plastic hanging from a spoke on the front wheel, like a very small bar end plug but with a kind of inverse of a hook (hook shaped but made of space) just beneath the bit that would be visible if it were a bar end plug, the lid if you like.
Obviously a photo would make this too easy for Brommie people to identify. But all help much appreciated in helping me figure out where it goes.