Citroen c1 making a rattling noise when I drive uphill or break

katie.dugmore that will depend on the exact location as well as the noise itself. It is possible that this is caused by a loose heat shield that will increase the vibration as there is more pressure on the exhaust pipe. Take a good look at all those shields. It might also help if you post lots of picture of what you see with your question. For that use this guide it will let us see what you see. If you are really talented you could even make a recording of the noise and post it (youtube.com etc.) and then let us know the link to the file.