The basic premise is you want to trigger some action (showing the loading symbol) when and only when the user reaches the part of the page where it exists.
There are some JS/jQuery plug-ins that do just this: tell you once a page element is visible on the screen. This has been worked on a lot so I’m just going to give you a good Google query result that you can look through for some possible solutions: https://www.google.com/search?q=jquery+visible&oq=jquery+visible&aqs=chrome..69i57j0l5.1842j0j7&sourceid=chrome&espv=210&es_sm=122&ie=UTF-8#q=jquery+element+in+view&safe=off
I’m not sure what your experience level is with JS/jQuery but I’m just going to give you a gentle push in the right direction as I don’t have time at the moment to write up a more detailed response.
Cheers