[DMcMahon]

Thank you for those inputs. Unfortunately my friend who owns the 4000 likes to do a lot of microphone recording and from a couple of microphone recording tests I have done, the recorded noise is noticeable.

I have not yet had a chance to do any more investigations, but having just done a quick conversion calculation from ibf to Newtons, realise that something is incorrect, as the average of 76 - 85 ibf is around 360 Newtons which is far too high (I thought 75 - 85 ibf sounded high) ?

It is certainly sounding like a NOS Drive Wheel may be the only way forward to improve the noise level. There are some second hand ones on eBay.de where they say they are good condition, but that is probably a large risk.