This sound effect can be found on Earshot SFX by DXM Productions. It is a low pitched and edited stereo version of ANIMAL, CREATURE - LARGE ANIMAL GROWL 02 from The General Series 6000 Sound Effects Library. It plays normally while gradually fading out on the left channel, and a reversed version that gradually fades in plays on the right channel. Links: https://soundeffects.fandom.com/wiki/Earshot,_Monster_Snarl_Pan#Audio_Samples