Thanks for all of the replies everyone. I did strip it down, regrease along with a bit of oil to thin the grease down a bit and it is still as noisy as before. I've made a youtube video of it running off of the machine so you can hear it, with it bolted on the machine it resonates and makes a much louder vibration and racket. On looking at the communator contacts they do look pretty worn and scored, I've given them a clean but it has had no affect on the running.
youtube link here:
https://youtu.be/iOx5711WORo
Any ideas?