Desperate for help with noise from rear

[wooly]

Bit of background guys bought a 2003 2.2 auto with 44 thousand miles at Xmas due to a knee operation barely drove the car. Noticed just after purchase a noise coming from the rear left side the noise is like driving over rumble strips.
Four different garages cannot find the where it's coming from two of those are bmw indy garages. Of those two have drove the car and acknowledged the noise is there when slowing down and coming off the accelerator.
What I have found is both rear wheels are not holding air it's got the original 108s on it with new Bridgestone potenza run flats all round. A local tyre place has repaired a crack in the drivers side rear wheel although it's still not holding air and this week the same place cleaned the rim of rust from the passenger side rear.
Took car out last night put air in both rears as they were below 30 psi it drove fine no noise for a little while then noise came back .
Could the noise be from the tyres loosing air rapidly I've heard run flats are noisy even when fully inflated any help really appreciated guys.

 

[Ant]

borrow a set of non rft wheels and see if the noise goes away is probably a quick solution

 

[Mike6]

Most people say ditch the run flats as all sorts of problems with these tyres. From what you say if you inflate to correct pressure noise goes away but returns as air escapes, this must frankly be the cause of the problem. An imbalance of pressure will mean car drops on that side and this must effect the suspension geometry which will probably make a slight noise which amplifies itself in the cabin. Sort out the problem wheel and I would quess your problem also sorts itself.