I heard some grinding noises when riding in the highest gear a few days ago. First I thought it was the derailleur. But it turned out to be not the derailleur. But it was the SA hub, which needed a little tweak.
I tried watching the Brompton Technical Videos to figure out how exactly to do it. But following their advise didn't get me the desired result.
Do you run into this sorta thing ever, with your Brompton, or with your 3-speed IGH? I would love to hear what you did.