General :: Hard Drive Thrashing With EXT4

I'm dual booting Ubuntu 9.04 and 10.04 on an ASUS P5VD2-MX SE mobo with 3 hard drives, a couple of DVD writers and a multi memory card reader (USB).

The hard drives are:-
1 250Gb SATA MAXTOR STM325082
1 80Gb PATA HITACHI IC35L090AVV207-0
1 80Gb PATA MAXTOR 6Y080P0

9.04 lives on 2 ext3 partitions of the 250G SATA
10.04 on the 2 ext4 partitions of the 80G MAXTOR
The HITATCHI has 1 ext4 partition mounted as a common data area for each O/S
The 250G drive has GRUB Legacy in the MBR with its files in a small ext3 primary partition chainloading the 2 O/S's, GRUB Legacy for 9.04 and GRUB2 for 10.04. It also contains the common SWAP partition (primary)

When I boot into 9.04 everything works as expected with as far as I can see no unusual disk activity even when the ext4 data partition and the 2 10.04 ext4 partitions are mounted. When 10.04 is booted however, after about 5 minutes (irrespective of whether or not the other partitions are mounted) I see the hard drive activity light come on and stay permanently on. The system monitor shows nothing unusual. dstat doesn't give any clues either. I've tried running iotop but it fails with a missing CONFIG_TASK_DELAY_ACCT error.

Is this a known problem with ext4, should I rebuild 10.04 onto ext3 partitions? Are there some special ext4 mount parameters I should use? (I simply copied the fstab lines from 9.04 and just changed ext3 to ext4). I've read that the journaling process(es?) for ext4 by default commonly access the drive(s) every 2-3 secs but that should just cause a flicker surely.