My protection circuit transformer started buzzing: bad component choice, or random failure?

I installed my own protection circuit into a Bose 1801 power amp. After I used the amp for a week or two, the transformer I installed to power the relay started buzzing loudly.
It is a loose mechanical sounding buzz that changes or goes away when I rotate it, press on it, or tap on it.

I don't think I overloaded it but want to check with people here to make sure I didn't do something wrong before I chalk this up to random failure and reinstall a new transformer of the same part #.

The transformer is a 186B36 and it powers a big LY4F-DC48V relay. Transformer is rated for 6.12 VA/170mA and the relay coil current is 30mA. That seems like plenty of headroom. But I don't want this amp to come back with the same issue, so here I am.
 

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