Just back from a ride and chanced to look under the rear mudguard and spotted the seat release cable had been touching the rear tyre whenever the suspension compressed. Checked under the seat thinking I might be able to pull the extra slack up under the seat but to do so would make the route rather acute and cause problems down the line. Best thing would be to remove the seat catch and trim the cable length - another little job for tomorrow! Might be worth checking to see whether you have a similar issue.