High pitched rattle - NOT timing belt/chain issue

[Mick Winstanley]

Hi; I’ve a 2011 61 plate A3 Sportback 2.0lt TFSI Quattro and there’s a high pitched but not loud rattle from underneath the car. Local VAG specialists say NOT a timing chain/belt/tensioner issue but likely either a loose Cat/exhaust heat shield or a noisy Turbo bypass valve. Car is otherwise in superb nick and done only 62500 miles. Any thoughts?  Cheers. Mick