As a WordPress developer, I see this is common in WordPress. I am pretty sure that it's not hacking attempt.
Note: Make sure to check your traffic logs for the sources of traffic that visiting this page.
It's called WordPress Heartbeat API.
WordPress uses it to manage functions such as Post Locking and Auto Saving etc. Some WordPress developers also use this API to make their plugins or themes functions, too.
The more you access your dashboard or leave it idle, the more Heatbeat API sends request to wp-admin/admin-ajax.php Heartbeat requests.
If you're active working in your dashboard, Heartbeat requests will have a max 60 seconds in each request delay.
If you put your dashboard sit idle, it will have a max of 120 seconds in each request delay.
You could DISABLE it or Increase delay time between each HEARTBEAT request.
Just a hint, disabling it could cause issue with functions that use the API.