I've only just started using the 11 May build and I noticed several times the past hour when clicking in the waveform seeker, sometimes the track would drop in volume drastically (sounds like 5-10% of full volume). I had volume set to around 50-80% in the program. Clicking on the volume slider fixes the issue whenever it happens. Clicking elsewhere in the waveform seeker again also fixes it, as does the track changing.
I've confirmed this isn't my hardware, as it happens with both my speaker and headphones outputs (and it's a giveaway that it resolves by clicking on the volume bar, or the waveform seeker).