iMac keeps searching external drives for apps?

Odd new problem here.

Every time I choose right click and 'open with' for any particular file whether it be a movie, an image file or whatever my iMac wakes up all my 3 external drives spinning the disks searching before the 'fetching' for the suitable apps list is populated. This can create quite a time delay before I am able to open said file.

I have added all 3 external drives to be excluded from any indexing or search in Spotlights preferences yet this continues to happen. Even at random times when I am doing absolutely nothing the iMac wakes up the drives and there is some activity going on. One particular drive is the worst with nothing on it at all except an inactive clone of my entire iMac's hard drive made with SuperDuper and there are no automated or scheduled backing up processes set up at all.

Why does this iMac insist on searching external drives for standard Apple/Yosemite apps that are on it's own internal Fusion drive?

How do I tell the iMac to just leave them alone?