Anyone know this sound?

Hi everyone. My electric hot water tank has started making a bang/clang noise every time it refills and is heating the water. For example, after we have fused the bathtub. I had a plumber come who did hear the noise, but wasn’t able to diagnose what the issue was. He recommended draining and flushing it, which he did, and he also checked the T&P valve as well as confirmed that the expansion tank was installed properly.

I was able to get the sound on video so I was hoping someone might be able to tell me what it might be? Thank you.