Whining noise rear right handside when accelerating
 

I have read many sites trying to find the answer to my dilemma.
When I accelerate past 30mph in my 03 Boxster a whining noise from rear right handside is heard and remains constant.
The noise stops when decelerating below 30 mph and is not there at low speeds under 30. It sounds awful but car drives well.
Thought it might be wheel bearing but got this checked out by mechanic and it wasn't.
They couldn't find a fault and didn't want to charge me a load of money taking the car apart which was nice!
Need to get it fixed and want to take it to Porsche Specialist with information so I don't get ripped off.
Thanks

I see that you are in the UK, and am guessing that the car is RHD.
If the car was LHD, the smart-a$$ in me would say, "stop taking your mother-in-law for rides". :D :D

Seriously, haven't seen this problem yet. Does the noise sound like it is more from the outside of the car or the inside? Secondary air injection pump is on that side.

Whining noise rear right handside when accelerating
 

It is definitely outside and behind me and yes it is RHD. Problem with all these sites are that so many noises mentioned it will take for ever to read all the posts.
Have sent a few messages so maybe I will get a reply with a positive result. My mother in law is lovely!! She spoils me Lol!
Have to say that as the wife will read this message I know!!

you need to isolate the noise so you can tell if it is the wheels/drive train or the motor (IE vacuum line, bearing on water pump/AC/Idler pulley...).

The easiest way to do this maybe not the safest is....

Open road, drive the car until the car makes the noise, take it out of gear and coast, if the noise still there? Now turn the motor off, careful not to lock the wheel and crash. If the noise is still there, it's the wheel bearings.

Aside from all of this, it is most likely the wheel bearings anyway. The right rear is know to go out repeatedly for some reason. If it is in the early stages, a visual inspection will not reveal a fault. I have been through two of them already.

jhandy's advice is solid. If you suspect it to be the wheel bearing after doing what he's suggested, jack up the back end of the car and make sure it's very stable, then have someone you trust get in and fire up the motor and put it in gear and get it up to 30 mph+ while you keep your ear close, but not too close, to your back right wheel.

Then shut of the motor and let the wheels spin and listen. Being able to get near the sound is really helpful.

This is what my mechanic did to determine if my rear wheel bearings were worn and needed replacement. I was in the driver's seat and he was by the wheels listening.

Whining noise rear right handside when accelerating
 

Thanks for all your advice. Finally the garage fixed the problem. They stripped brake disc and caliper adjusted and cleaned back plate assembly. This reduced the noise but it was still there slightly so in the end they did replace the rear whell bearing and now all is well. So wheel bearing it was!!!
Cheers