Galaxy S5 :: Stopping Hangouts Vibration For New Texts

I started using Hangouts again for SMS on my Verizon S5 and quickly remembered why I had stopped in the first place. I cannot seem to turn off the Hangouts app vibrations for new texts. See, I use Light Flow for all my notifications, and I have it set up to vibrate twice when I get a new text message. Light Flow is working fine, but the problem is that there is always a third, longer vibration immediately before the Light Flow ones. I assume it's coming from the Hangouts app itself but I've poured through every setting, turned off vibrate everywhere I've seen it, and yet the single, long vibrate persists. I've even gone through all the main phone settings to no avail. I'm also relatively certain that Light Flow isn't the issue; when I disable that app, I still get the single, long vibration from Hangouts.