As mentioned current model 24" iMacs do not have spinning HD's, they all use SSDs therefore the storage has no moving parts. About the only moving parts I can think of in a 24" is the fan assembly and I have never heard of one "ticking". My guess is the OP has some type of notification or other sound turned on. My recommendation to the OP is to contact AppleCare for assistance or to provide an EtreCheck report where we can look for any obvious software issues.
To the OP:
It will help us get a good idea of what is causing your problem if you provide a report of your system, that way we do not have to play 20 questions with you. The report we are requesting does NOT provide any personal information and is extremely safe to use. Please navigate to www.Etrecheck.com and download the free version of EtreCheck. Once you have you downloaded the app and installed it, please run the report and save it.
When you have your report, you can attach it when you reply to this message and we can then review it and help you determine what is needed to get your system running well again.
For instructions on how to download your EtreCheck report and attach it to your reply to this message please click How to use the Add Text Feature When Post… - Apple Community