In the Irish course, there is no audio in any of the "type what you hear" questions. The others all work, only this particular type of question has no audio.
As far as I know this type of exercise only works in the Duolingo website, and you don't get "Type what you hear" exercises in any of the various Duolingo Apps on mobile devices and tablets. In that case, have you tried to use a different web browser - Microsoft Edge, Internet Explorer, Firefox, Chrome?
Do you get "Type What You Hear" exercises in French or German?
Have you checked the Account Settings in the drop down menu next to your name in the toolbar - there are some settings there that effect the audio.
When you submit some sort of an answer, you get two buttons - "Report" and "Discuss". If you click the "Discuss" button, does the sentence have a blue speaker icon next to it, and does the audio play if you click on that icon?
Can you tell us which sentences you encountered this problem with?
I just did a slew of lessons and tests in three different units and got the audio test questions quite a few times. Each time the audio worked correctly. If it's not an issue with your Duolingo settings, try using a different browser as SatharnPHL recommends.
If the problem persists, you should probably post this in the Troubleshooting forum to get more detailed technical support, because I don't think it's a problem with the Irish course itself, but an issue either on your end or something with how your PC is connecting to the website for whatever reason.
I occasionally get this issue with Safari on OS X. My fix is just to quit Safari, clear history, and reopen. The audio then works for 'type what you hear'. Why only this type of audio file seems to be affected I'm not so sure about but probably has something to do with how the file is 'called'. If you're not on a mac, try clearing your cache and reopening anyway, it can't hurt to try hitting the site with a clean browser.