I put some powerflex poly bushes on my exhaust, it was banging no end. Its solved it apart from really bad bumps.
Apparently all other normal bushes can flex slightly even when new, these were only a fiver from halfords, or any other internet site.
Didnt solve the lumpy idle and temperamental 'i will accelerate smooth when i feel like it' bad attitude from the car though
Incidentally to fit them. The old mounts are a simple bolt off, but the old mounts have a tube which is similar to a rivot at both ends ie tapers out, which i had to grind down and replace with a normal nut and bolt.