So I squirted a bit more WD40 in. No difference. Made an audio recording too.
https://soundcloud.com/natangora/engine-squeal
Just squirted a whole load more WD40 into the tensioner bearing. Will leave it for 10 minutes then try again.
The more I listen to it though the more it sounds like it could be coming from the area just behind and to the left of the serpentine belt.
For what it's worth I also took a few photos of the hose with the split in it
https://www.dropbox.com/sh/77yz090zitg9s9p/id0Hm_YtDn

