Brompton's response is odd. be careful of it. The hub gear does make an increasing ticking noise going up through each of the 3 internal gears, nothing like a rubbing mudguard. It is also louder as you go up the range so 1st should be the quietest from in the hub - mine in 1st is silent.
I live in a hilly area and have a bad knee. I use my 1st gear a lot, there is nothing different in the sound and pedal feel in 1st that in 2nd or 3rd - apart from the louder ticking from inside the hub going up to 2 then 3 and it is literally a ticking noise like a clock.
I'm not totally sue on the derailleur on a Brompton do they have hi-low limiter screws like a regular derailleur? if so then a rubbing noise in 1st and rough feeling chain both suggest the derailleur is misaligned and probably moving too far in and ever so slightly catching the spokes?????