Loud rhythmic humming on stacked Quatro 10kw inverters

I have an install where I have 4 10kw Quatros in a split phase configuration. The problem I am having is when the inverters are using the grid to charge the batteries (6 ea. 48 v 200Ah) when the inverters switch from bulk to absorb, the Inverters start a loud rhythmic humming with a “Ticking” sound. The sound is not heard when in bulk charging.
Has anybody had the same issues, and if so, how was it corrected.
Thank you for your response.
Dave

Can you upload a recording? I have the same configuration, of the same inverters - happy to compare.

Hi, I have a humming sound on a QUATTRO 48/15000.
Is it the same?