Got it back. No charge. I think they washed it

The chap who called me on the phone to tell me they couldn't hear any noise came out as I was leaving. Revved it to 2k as explained, let it decelerate, noise was audible. He said 'oh yeah I hear it'.
Off to the tuners we go. Milltek non res and a stage 1 incoming, once this little noise is sorted!