Blown Woofers in Matrix 802 S3

I have a quetsion I hope someone out there can help me with! I have a pair of B&W Matrix 802 S3 speakers driven by a Musical Fidelity M3 Integrated Amp. Has worked very well for many years. Source used to be MF 3D CD Player but now is computer based via a Logitech Duet to a Benchmark DAC 1 and into the amp. About eight months ago the lower right side woofer started making a scratching sound - I assumed it was blown/damaged from old age and replaced it with a new one from B&W. Problem fixed - or so it seemed. Just yesterday the new woofer on the lower right hand side has developed a similar scratching sound. My question is this - what is the likely root cause of this? Given the other three 15 year old woofers are working perfectly yet the new one has developed the same problem as its predecessor. Could this be caused by an ageing crossover? What else should I look at/test to find the root cause before once agin replacing this woofer? Luckily I bought two woofers at the time - one for insurance - as I really do love these speakers - I just do not want to have the same thing happen to it! Any help or guidance you can provide is much appreciated.