Air con - similar experience
I have had 2 different 159s (first one got stolen) which developed the rattle/grinding noise and were cured with re-gassing. On the second car it recurred very quickly so I took it back for checking, and the technician reported that there was a release of pressure on removing the dust cap on the low pressure side and confirmed low gas - so he regassed with some fresh PAG oil and it has been fine ever since - about 7 months since the last refill.
Go to FI Autocentres - they did not charge for the second re-gas and only charged just over £40 for the first one - and did it while I waited. With this experience I would certainly try the regassing before swapping parts.