Droning noise from rear
 

2008 V70. Slight (irregular) droning noise from the rear at motorway speeds, but only when there's a rear passenger on board. Not emanating from the passenger. But seems to be coming from the same (nearside) corner as the passenger.

The year before last there was an MOT advisory - trailing arm bush deteriorated, but not excessive. Though I'd imagine that wouldn't produce this sort of noise?

Only 71k, though very crashy over potholes. I understand that this wasn't this model's best feature, even when new, but have been thinking about replacing the shocks (with Sachs?), despite the low mileage, on the basis that they've been compressed by a heavy vehicle for 11 years now.

Any thoughts gratefully received.

drone
 

run your hand along the inside edge of rear tyre,as if it was turning on the road-if it feels rough/saw toothed it will drone-possibly worse with load as this will increase the load on inside of tyre

Many thanks - will do so (if it ever stops raining for a moment)

Rather than "drone" mine had an irritating squeak, without passenger and only when the weather was dry. It was the trailing arm bushes, which by all accounts last about 70k ish, replaced and all good.
If you do replace them then factor in for all wheel alignment as the rears will need to be done/checked........at a dealer around £400 I think all in.

Droning noise could also be a wheel bearing.........

Had a similar noise on my S80 Saloon a couple of years back. It seemed the rear disc caliper was binding at speed causing the noise. New calliper discs and pads cured the problem.
How this helps.

Rear wheel bearing? The extra load of a rear passenger could induce the noise.

I had both the rear wheel bearings replaced on my 2010 XC70 which has a similar mileage to yours, and the droning noise was cured.

Thank you to all - the suggestions are much appreciated - will investigate and report back.

As tony says, check for sawtooth tyre wear.
Caused by misalignment of rear wheels, so the rear tyres vibrate. Mine did this when I got it, cured by new tyres and a 4 wheel alignment.

You stated in your first post.........40t that is........

"The year before last there was an MOT advisory - trailing arm bush deteriorated, but not excessive. Though I'd imagine that wouldn't produce this sort of noise?"

So if the tyres have sawtooth wear is that down to the trailing arm bushes being worn ? Hence out of alignment.....just an educated guess.....
Getting it aligned with worn bushes might cure your problem for a short time but, they will wear more quickly and you end up with the issue again me thinks, on possibly new tyres if fitted.

Your shout not mine..................

In theory nothing should go out of alignment unless you have worn or bent suspension parts (potholes spring to mind on that one).

New (front) tyres fitted today - slight flat spot found on inner edge of rears. With thanks once again to all, it does seem possible that trailing arm bushes could be the cause. No bearing noise detected, though noted from the helpful comments that this does not rule it out.