Audio Research VS110 Power Transformer Buzz

I have a problem with my Audio Research VS110. The power transformer starts incrementally buzzing after 15-20 min of use and becomes louder. At the beginning there is no noise at all. The noise is purely mechanical from the transformer (no buzz is coming out from the speakers). This buzz is due to magnostriction. Typitically this is observed from the beginning, and this is what puzzle me. I am afraid to leave the amp in operation more than 45 min/hour in case I do a more serious damage. 

History: The chassis of the amp was damaged during transport of the amp and was replaced.  I wonder if the transformer needs to be replaced because of a defect or this is due to a re-connection mistake occurred when the chassis was replaced.

Your advise will be greatly appreciated.


Thank you!