said by fegul:I had been having issues with Hangouts where it wouldn't ring reliably within GMail if the user was on a different tab. I'll check to see if there's a way to fix that.
It's not my area of expertise, but if you can't find an easy fix, I'd try opening Gmail in a separate instance of Chrome, where it's the only tab. Or, try it in Firefox (if your normal browser is Chrome), or vice-versa.