We’re rewarding the question askers & reputations are being recalculated! Read more.
3 of 7 added 683 characters in body

MATL, 37 36 bytes

0`Q4\'Loading... 'y'|/-\'w)hD2.5&XxT

Here is a gif recording from the offline compiler:

enter image description here

Or try it at MATL Online! If it doesn't initially run, refresh the page and press "Run" again.

How it works

0                % Push 0: initial valur of counter
`                % Do...while
  Q4\            %   Increment modulo 4. This avoids overflow
  'Loading... '  %   Push this string
  y              %   Duplicate counter
  '|/-\'         %   Push this string
  w)             %   Swap. Select the character given by the counter
  hD             %   Concatenate the two strings and display
  2.5&Xx         %   Pause for 0.25 seconds and clear screen
  T              %   Push "true". This is used as loop condition, to it
                 %   generates an infinite loop
                 % End implicitly