1- Lean by the pedals looking up
2- Remove the carpet cover by carefully unclipping the two plastic fasteners (careful: do not pull all the way because it has cables attached)
3- Reach out with a 10mm socket using an 8 inch extension (or 2 x 4" extensions) since it is a bit up there
4- Unscrew the bracket (it resembles a number 4 as in Tom's pic)
We shall name it "Rattle number 4"?
Link to pic:
Misc - Alex Franic Photography