It's scanning the drive for files. I have a 16GB microSD card that I sync fairly regularly and it will usually take 3-4 minutes, so 10 minutes seems a bit excessive if that's really the case.
You might try reformatting the drive and starting from scratch. Maybe try a different filesystem like exFAT if all of your devices are compatible. You could also try a different USB port.
It could also just be a slow flash drive.