iTunes is adding my sample library to its library, how do I undo this?

Hi, my 140Gb music library is stored on my iMac.

I've finally got it all uploaded to iTunes Match and am now activating iTunes Match on my Macbook and Windows laptop, as I want them to be simple 'slaves' to my iMac's music library, so they can stream its music when I travel.

When I opened iTunes on my Macbook, I needed to do a 'search for music' to get my artist tab working.

As there is NO music in my 'automatically add to iTunes' folder, I was very surprised to see my Macbook's iTunes started adding all my samples for Ableton Live, which are stored in a Dropbox folder.

My iMac has an identical folder structure and has never done this.

My Macbook now has my entire iTunes library viewable on Match (great) but with hundreds of drum loops added too (not great) which I imagine it will now start trying to upload to the iTunes Match service (even worse).

How do I remove these samples from my iTunes library on the Macbook without deleting the real ones; and stop it happening again?

As far as I'm concerned, no music that is not put in the 'Automatically add to iTunes' folder should ever enter my collection.