You should consider running a dedicated grounded circuit to your audio system.
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A DC filter may be what is required. The inductance of the trani is a short to even tiny amounts of DC voltage on the line side, and it causes the trani to hum, because the low DC impedance will cause a large DC current. There are plenty of DC blocking filters available. Search this website for info on DC filters, info galore.
As the noise is mechanical in nature, ie not in the speakers, this is the most likely cause.