This is probably a very basic issue, but I can't figure out why these dots around the text boxes are visible on the exported PDF file. They are not even visible in the InDesign source file.
Ok guys, solved it myself. All boxes that have these visible frames have transparency flattening issues, after exporting it to pdf (adobe pdf preset earlier than 2005).
When I export it to .pdf 2008 it works well - no frames.