Thanks for all of the input guys.

Although the noise sounded like atsmopheric noise, part of me thought
it might be something else...and I turned out to be right. After
staying up half the night, I discovered a laser printer that had been
left turned on in a different room. I turned the printer off, not
really thinking that it would be the cause of the noise on the Drake.
But when I then walked into the room where the Drake sits, it was on
and there wasn't a trace of noise. Just for the heck of it, I had to
turn the printer back on to see if the noise returned...and it did.

It's amazing to me that the Drake could have been affected so much more
severely than the Lowe by the noise from this printer, but now I'm just
glad that the noise is gone. Everything sounds the way it should now.
Steve