Help with buzzing mains transformer

[carbondated]

Have a quick question. The RH807 amp, which has been running beautifully for about a month, has suddenly developed a buzzing sound coming from *inside* the chassis (not through the speakers) after about an hour of running. I've narrowed it down to the power transformer (Lundahl 1683). It comes on after about an hour of use and stays; it's a pretty loud mechanical buzz, rather than a hum. If I switch off, wait five minutes, it's okay again until an hour later.

The transformer is followed by a 5U4GB rectifier (rather than the GZ34 in the schematic), 47uF cap and two 50mA chokes, another 100uF pair electrolytics.

Would appreciate any ideas...

 

[korey]

Sometimes the laminate plates rattle from magnetic vibration due to the transformer not being tightened down properly.

 

[amptech]

Does the transformer buzz if you float the secondary wire's off load? sometimes you can soak the transformer in hot varnish and leave it to dry out..

 

[carbondated]

Contacted Lundahl directly and it turns out there was a faulty batch of 1683s - Per Lundahl himself got back to me and they immediately dispatched a new one the very same day