Finding source of disk activity?

Hi there!

Okay, simple summary; I've got an external drive that I use for downloading large files, and for music (to reduce activity on my main drives), and this is exclusively used by Transmission (bittorrent), and iTunes as a result. However, very rarely I can hear the disk thrashing away, and this will continue even after I quit both programs, the only way I can seem to make it stop is by unmounting the drive and remounting it again.

I'm wondering if there is an easy way to see a list of running programs and the amount of disk activity that they are generating? Per-volume would be nice but even a simple readout of processes should allow me to zero in on the culprit. The only other way I can think of would be to quit processes one at a time until I find the perpetrator, but I really don't want to do that if I can avoid it!

 

I know what you mean about the Finder I think, annoys me when my other external drives spin up all the time when I don't need them every time I load/save

But in this case it's proper disk activity of some kind, a lot of thrashing but no obvious cause as nothing is being written, and nothing should be getting read.