AudioClip concatenation

Linux 6.1.38
Python 3.9.17
Audio device: Advanced Micro Devices, Inc. [AMD] Family 17h/19h HD Audio Controller

I am composing a sound as follows:

silence = sound.AudioClip.silence(duration=0.180, sampleRateHz=44100, channels=1) 

beep=sound.AudioClip.sine(duration=.020, freqHz=1000,sampleRateHz=44100, gain=1, channels=1)

both=beep+silence+ beep+silence+ beep+silence

When I save this sound as wav, flac, ogg and look at it with audacity, the beep starts at time 0.0 ms as it should. When saved as mp3, the beep starts at 25.0 ms (prefixed with silence). Is this as expected?

It appears that the internal sound (in psychopy) does start at 0.0 – the worry would be the start delay using the mp3 file once saved rather than generating it in the experiment.

saving just the beep gives (using soxi)

flac Duration  : 00:00.02 = 882 samples = 1.5 CDDA sectors
wav Duration   : 00:00.02 = 882 samples = 1.5 CDDA sectors
mp3 Duration   : 00:00.05 = 2293 samples = 3.89966 CDDA sectors

all at Sample Rate : 44100 Precision : 16-bit