Twitterific causing Voiceover to make noises when phone locked

iOS & iPadOS

iPhone 5S, latest iOS8, latest Twitterific. When Twitterific is running and the phone is locked, every once in a while, it will cause Voiceover to make a VO noise. Sometimes it's a high chirp, and sometimes it's the loud bang that means you're at the end of something. Closing Twitterific in the app switcher fixes the problem. I've tried turning Twitterific's background refresh off, but the setting doesn't stick, it turns back on immediately. This is most annoying when you're listening to audio, as it activates audio ducking. Any thoughts? Thanks.