It was on ADSB Exchange but not Plane Finder. Out of Shannon and went into Ostend (or somewhere along the Belgian/Dutch coast, I didn't look that closely!). Definitely sounded strange, rather a grinding noise. I actually thought it was a much lower piston engined aircraft at first - got a glimpse of its lights through the odd gaps in the cloud!
Islander G-BLNI came past on its way into Biggin a short while later... they always sound slightly out of synch!