Getting out of iowait hell

I have a problem that's really got me baffled. Some mornings when I get up to start work, I find my laptop is extremely unresponsive.

I ssh into it to have a look and see that the CPU is saturated with iowait. However, I can't for the life of me figure out which process is causing the problem.

The closest I've got is pidstat -d which should show IO hit on a per-process basis, but that doesn't seem to reveal anything of any significance either.

Any ideas?