No fast music at chain of 40?

Question

After watching a handful of videos on shiny hunting in Pokemon XY, I've decided to try chaining using my pokeradar. Last night I managed to reach a chain of 40. However, the fast music didn't turn on as expected. I decided to continue encountering Pokemon, but at chain 45 the fast music still wasn't making its appearance. I'm almost certain I didn't break my chain in between, so is it a glitch or am I doing something wrong?

Answer 1

Fast music doesn’t always play at a chain of 40.
Fast music appears at random, not at a chain of 40. It’s not a glitch.

Source:Got multiple pokeradar shinies