continous high pitch noise, please help

[Yaron]

Hi
I have an mbox2 running PT 8.0 on an iMac 10.5.6 with just YAMAHA HS50M powered monitors and nothing else connected to the system. Whenever I launch ProTools, a rather loud, high pitch whistle starts in the launching process even with the monitor and out knobs of the Mbox2 all the way down. it does not show on any meters in sessions either. when the playback engine window is up, any change to buffer size or other setting stops the noise until hitting OK on that window then it comes back again.
any ideas? anyone?

[Top Jimmy]

Use TRS cables.

[amolin]

I had the same problem, but when I got balanced cables from the mbox to the monitors, it was gone.

[Yaron]

Thanks for the info, got the balanced cables and they reduced the noise to an almost manageable level but not completely, that high pitch is still noticeable and reacts to playback engine changes. any other ideas anyone?

[Jwald]

If you have a power conditioner, plug your computer into that, this is how I got rid of my ground hum. There are also de-hummers available, but they cost between $50-80. I hear Passive DI's also get rid of (ground) hum.