raid5 + LVM2 + ext3 (+ netatalk) == choppy read times? HELP!

I have recently installed Debian Etch r2 on a box with 5x250GB SATA drives. I've raided those drives in a raid5 configuration, then made a logical volume group and formated the group using ext3. I've noticed that once I tried to stream data (music and movies primarily) off of the box (through AFP/netatalk), that the data stream is choppy. Once every 10 seconds or so, it 'hiccups' and the stream is paused, or extremely slow, for about 1-2 seconds. The box seems to write data just fine, as I've tested by copying over 300 gigs at a sustained rate of 10 MB/s.

I'm fairly new to linux, and don't know a tremendous amount about server optimization. So far I've run a series of iostat reports while streaming data off of the box and saved those results (attached to this doc). The problem doesn't seem to be CPU related, as the iowait is only at around 1.6%. I don't have many other services running, as this is first a data server for a single client (me).

I've also tried searching around for a possible solution to my problem, but haven't really found anything yet. I'm still not sure if the problem is the partition type, the raid setup, the sata controllers (and/or drivers), or my netatalk setup. I've compared my setup to a similar box (built with etch r1) that seems to stream data just fine.

Any help will be greatly appreciated!
-Mike W.

PS. As per my iostat results: sda is my boot drive, while sdb-sdf is the raid.