Voltage converter 110-220V

I have a high end preamp 220V from Korea.
When I used this audio with transformer 110-220 3KW, I could hear noisy and it became worse. I sent it back to Korea(220V) to repair it but in Korea 110V there are not any noisy and no problem at all.
I guess the step up voltage 220v is causing the noisy.
Please help to solve this matter if anybody has experienced the same problem.
I wonder if some special transformer is necessary.
Just as a test, try lifting the ground plug on your preamp power cord. Use one of those cheater plugs that will allow you to use a two prong socket. If the noise goes away, you are probably looking at a ground loop. If it does eliminate your problem, "don't continue using it this way. It is not safe but it will tell you if you have a ground loop problem.

On another note, most transformers allow for 110 and 220v connections. Did you ask the manufacturer? If not you could have the transformer changed to a 110v transformer. Step-up and step-down transformers tend to cause some issues.