Is there any way I can switch off the "small image" file from all my playlists ?
You can remove any column from a list view.
As all my music is stored on several usb hard drives and my sound card is also usb, the caching of the image files causes pop and clicks during playback and frequently cause the sound card to cut out altogether, with an unpleasantly loud pop through my speakers.
Are you using USB1? USB2 shouldn't be a problem (ar least not because of too limited bandwidth), but naturally there can be other factors, like badly behaving chipsets, drivers etc.
What exactly do you do when the problem occurs?
Once the thumbnails are build they should not cause any problems. Have you tried to prebuild the thumbnails? (Tools > Options > Tree & View > Thumbnails > Build missing thumbnails)
I can remove the images individually by scrolling through a list, but I have a lot of playlists, so would like to change the default setting to no "small images".
What exactly do you mean by "I can remove the images individually"? Do you use the "Remove cover art" feature or something else?
EDIT
I think I got it: you are already removing the image columns, but you must do it in each playlist separately.
As gappie said, I don't think it is possible to change them all at once, but you can save the column setup as a preset and load it in another playlist. Right-click the column header row to quickly access the preset feature.