If you use Classroomscreen in your classroom to support class activities, you will know that there are built in audio sounds to the timer. While you can not add additional sounds to the timer - you can embed a webpage with additional sounds.
You will then see the site on the screen. You can shrink or enlarge the embedded page as well as navigate between the 3 pages.
Embedded below is a 1 minute and 49 second YouTube tutorial.