When trying to burn a DVD it sometimes happens that growisofs will fail with:

$ sudo growisofs -speed=8 -dvd-compat  -Z /dev/scd0 -J -r .

Executing 'genisoimage -J -r . | builtin_dd of=/dev/scd0 obs=32k seek=0'

I: -input-charset not specified, using utf-8 (detected in locale settings)

0.23% done, estimate finish Fri Sep 16 14:49:33 2011

0.46% done, estimate finish Fri Sep 16 14:49:33 2011

0.69% done, estimate finish Fri Sep 16 14:49:33 2011

:-( unable to O_EXCL /dev/scd0: someone was in time to remount?

This only seems to happens when burning multiple DVD's in a row and I think it happens when I eject an automounted disc without manually unmounting it first, which implies that something is keeping the drive busy, lsof and fuser however fail to find a process still accessing the drive. Rebooting makes the problem go away.

How can I find out what process is causing this issue?