Pulse-audio (or maybe Alsa behind it) pitch shifts when opening apps or streams

Does anyone else experience this or know what causes this?
When I open audacity, or start a virtual machine, or sometimes when i watch a youtube video, the pitch of all audio changes, usually higher (people talking on youtube sound like they’ve had helium!) but sometimes lower. It then resets to normal pitch if I restart pulseaudio using ‘killall pulseaudio’.