I have been having a kind of rumbling whirring noise coming from the rear of my 2010 TD4 HSE since I bought the car around a year ago. It is only evident in over run. It didn't seem to be speed related. I serviced the haldex and changed the diff oil when I bought the car last August. This did not improve things. I have done a couple of thousand miles since with no improvement or worsening.
Today I decided to try and get to the bottom of it and did masses of research on this website and others. I was preparing myself for a hefty diff or haldex bill. However, there seemed to be a recurring theme in some threads of tyre noise. I found it hard to believe that this could be my problem, but hey ho, as others have said, start with the easy stuff. My tyres ( which were on the car when I bought it ) are Landsail Trailblazer CLV 2 235/60R 18 all round with about 5-6mm of tread remaining with pretty even wear imho.
I initially dropped the tyre pressures from 32 psi ( recommended by LR) to 25 psi and went for a short drive. No change, perhaps slightly worse but only on over run as always. I came home and inflated the tyres to 37 psi and again went for a short spin. To my amazement the noise had vanished. I was positive that the noise was mechanical.
Am I missing a trick, and by over inflating the tyres just disguising the noise from some other part being transmitted due to the reduced contact area with the road surface, or could this really be the solution ( new tyres not over inflation ). What do you guys think ?

The older the tyres get, & as the smaller the sipes get, the more noise the tyres make.

The cheapest option & quickest clarification whether it is tyres or not is get 2 new tyres for the rear (keep the old ones as they have 6mm tread). If the car is quieter the problem is solved. If there is no change, you have 2 spare tyres!

There are some comments on tyre noise in this thread: https://www.freel2.com/forum/topic33026.html Procrastination, mankind's greatest labour saving device!

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Thanks for that 😀. Interesting reading on the link you posted. Pretty convinced that a new set of tyres will prove / solve the issue. On the test drive yesterday I could hear a slight binding on one of the rear brakes, so have done them today. One upper slide pin was a bit seized. Sorted now. The next dilemma is which tyres to chose .......

Its a well known issue (on this forum anyway).
Never heard of Landsail tyres - if they are "budget, cheap as chips Chinese tyres" they may generate more noise than the norm for most tyres.

But even with premium tyres I've had "whirring" as they got near the end of their lives. New tyres solved the issue. Jules