Learn Turkish: Bu takırtı ne? Duvarı kazıyor olmalı. - What is this clatter? He must be scraping the wall.

If you said kazımalı, it would mean "he must scrape" in the sense of an obligation (he has to do it). By attaching the continuous suffix -ıyor to the main verb and moving the necessity suffix -malı to the auxiliary verb olmak, we get kazıyor olmalı. This creates an "epistemic deduction" meaning "he must be scraping"—a logical conclusion you are drawing right now based on the noise.

Is there a difference in meaning between "kazıyor olmalı" and "kazıyordur"?

Yes, though they are similar. kazıyordur means "he is probably scraping" or "I assume he is scraping." Using kazıyor olmalı is a much stronger logical deduction. You are saying "I hear a clatter, therefore the only logical explanation is that he must be scraping right now."

Does "kazıyor" come from "kazmak" (to dig) or "kazımak" (to scrape)?

It can actually be both! The verb kazmak (to dig) takes the buffer vowel ı before -yor, making kazıyor. The verb kazımak (to scrape) drops its final ı when a suffix starting with a vowel is added, which also results in kazıyor. They look identical in the present continuous tense. We only know it means "scraping" here because of the context of the wall and the clatter, though "digging" wouldn't be impossible!

How is the word "takırtı" (clatter) formed?