This kind of Ground Loop hum typically happens between certain laptops when using AC power and having that laptop connected to an external amplification system.

The hard drive should not really be the culprit, although it might be able to create a ground loop under certain circumstances, such as use of the larger Audiophile series drive with AC power. But the USB hard drive cannot create an AC ground loop if hooked up to USB only (no wallwart for power).

I'd like to know your entire signal chain, what is hooked to what and how, in entirety. That may help get to the bottom of things the fastest.

TIP: Set the system up as before and see if you still have the hum. If so, temporarily disconnect the Laptop AC power plug only and see if the hum stops when laptop is running on Battery power. Report the result here.


--Mac