For the record, I made this just to explore FM8, and learn more about FM synthesis, and a Skrillex bass seemed like a nice sound to try and get, since he does use FM8.
Sorry for the audio being so low, I have to sort that out.
Please also bear in mind that this is just a general guideline as to how to make a growl sound, try and learn from it rather than copying down all the things I did, it took me a while to figure out how to make this type of sound, so learn how I did do it, and it will help you understand FM8

Here is the tutorial, and if you liked it, please stop by my main channel "EoinOBroinMusic". Thanks