step up transformer noise

I purchased an amp from Europe that needs 240v [ I am on north American voltage].. I bought a step up/step down transformer to equalize the voltage. it works, but the transformer produces noise through the speakers, even when the amp is turned off. the transformer I bought was $60.. do I need one specific for audio applications? any suggestions?thanks for any help, dan
You can probably send your amp back to the factory and have them convert it to NA voltage.
Or a cheaper alternative would be to do as I have done - run a 240 wire to a new outlet. You'll have a dedicated power source and better performance.
Do a search here on Luxman as there is an in depth discussion on step up transformers and what works best.
Either that or as Zd542 offered, you can send it back and have it converted.

All the best,
You don't even need a new outlet. Google "240 volt split duplex receptacle (adaptor). Easy.