I've only just joined, hence v. late reply.
1. have you tried pop/click filter (Tool, Filter, Pop/click)?
If you don't want to process the whole file just select the section (left-click for start, right-click for end in v5.06) then click Seln in the toolbar. (If the left/right click method of selection doesn't work then set it in Options, Window) and apply Pop/Click to that.
You can keep expanding the display to home in on the offending section by selecting it as described above. At a certain point Pop/click will not work when the selection is too small.
Otherwise you can expand the section containing the 'artifact' and cut it out if doing so doesn't ruin the continuity.
Try the Smoother filter, but this will dull the sound
Select the section and try reducing its volume drastically
This is very tedious, but you can flatten or reshape the artifacts. I can't easily describe how to do this, but the manual is pretty good.