[carlg1212]

It's most likely 60Hz hum, the bane of our existence. The 60Hz hum could be from many things, such as a fan or refrigerator running, a bad ground, a noisy light in the room, etc. It can even happen from random electrons smacking into your headphones.

The pros spend the most time and money getting rid of noise issues relating to bad grounds. Sometimes, this means rewiring the electrical service in the recording studio.

There are software filters, but the best solution is to make sure your shizzle is grounded; touch your Mbox when you start PT, and if the noise goes away, it means you have a bad ground. There are many ways (some painful) to get a good ground.