Need Help - Hum Noise from Audio Research VS55

I have owned a VS55 for a while. The unit was fine when I used it in US. I like the VS55 sound so much and decided to bring it with me to Singapore. But when I hooked up the VS55 (via 220 v to 110 v transformer) to my Proac speakers, I heard a little hum noise out from the speakers. I do not think that the transformer is the issue as my CJ MV-55 works fine without the hum noise. Any suggestion from VS55 audiogon owner on what I shall do. Shall I change or roll the tubes to get rid of this hum noise sound?