Ok so had a local place fit the new downpipe with pre cat removed and if anything it;'s now worse.
The sound is evident on idle, it sounds very metallic, and then every time I release the revs it happens and now it's really loud.
Could it be the main cat its self? Sounds like loose metal mesh that's being ripped around every time I let off my revs.
Going to take it back to the garage on Monday to see what they say, but I'm now thinking turbo or cat etc? Performance is down, takes a while to spool etc, but I;ve bought a new diverter valve just in case also.