WR engine Ur quattro odd noise

[Colin Aitchison]

Hi guys, I have an odd bearing whine noise, but I know it is not bearing, please read on, when the engine is hot this odd whining noise comes and go's, I can get the noise to vanish when I open the oil filler cap slightly, now as this engine is a vacuumed sealed engine anything you do to let normal air pressure into the crankcase will have an adverse affect on the air flow metering flap and close it a little, even taking the dipstick out will make the engine run poorly, so back to the noise, it is coming from the rear of the engine below the distributor area, fitted new seal to distributor, in my mind this is a vacuum sealing problem and could this be the rear oil crankshaft seal or the alloy housing seal to the block on the rear of the engine, I do not have any oil leaks at the rear of the engine, as you are aware the box has to come off to get to this seal and is a 2 day job, do you guys have any thoughts.
Thanks in advance.