Mine turned out to be a failed front CV joint on the prop shaft (the grease had ‘baked’ and lost all its lubricating properties).
The front CV joint is serviceable but the centre support and bearing are not – so if either of these are shot you will need a replacement prop shaft.
When I got the prop shaft off I found the rear CV joint was also partially seized – so I needed a replacement. Problem is Volvo wanted over £1000 for a replacement!!!
I looked at getting a prop shaft from a breakers yard but found they also had the partially seized CV joint at the rear.
I eventually obtained a new replacement prop shaft from
https://desshelleyshafts.com/
It was delivered the next day, it has serviceable front and rear CV joints and the centre support bearing is not just serviceable but has a grease nipple provided. Cost delivered was around £360 and fitted it myself. I would expect a garage would charge about an hour’s labour to remove or fit.
When fitted not only had the noise gone but the car was noticeably smoother (as it should have been given that it had been running with a partially seized rear CV joint on the prop shaft).