Help identifying whine

[Kitchener]

I've had my Crack for about two months now, and I love it dearly.
Anecdote:
Pretty much my first foray into higher end audio.

I did a pretty decent job soldering it together, in my own most humble opinion of course.
I'm not entirely green with the soldering iron and took my time making sure each joint had a strong mechanical connection (I pity the fool who has to disassemble this Crack) and was nice and smooth.
Sure, the wiring isn't all neat and angular like some do it, but it's pretty decent.

I had one bad connection though:
One of the 3K 10W resistors had a flaky joint that got knocked loose.
-I guess I got tired and careless by the end of assembly.
This lead to a very noticable pop in the right channel whenever I tapped any of the connecting parts, and the right channel eventually crapped out entirely.
Easy fix.
Anecdote over.

But on to the matter at hand:


I've had a quiet, weak, high pitched whine coming from both channels (I think, it's so weak that I can't really tell for sure) whenever the volume is turned all the way down.
The noise goes away the second I turn the pot just a few degrees.
The noise is there independent of wether I have a source connected or not.
Swapping tubes, cables, whatever makes no difference.

The Crack is in my office.
Connected to the same outlet as pretty much every electronic device in it.
It's two-three feet from my two massive computer monitors.
Three-four feet from my desktop computer.
Four feet from my landline phone.
One foot from my ethernet cable box.
It's basically surrounded by electronics.

This is the only noise coming from my Crack.
I use my iPhone 6S Plus as a source, and there is no hum or any other noise with it connected, no matter how high I crank the volume.
Just the weak whine when the pot is turned all the way down.

It's not bothersome or anything, this is just for "fun".
-well, fun to me anyway.

What can it be?
Interference?
I'm betting interference.

[Paul Birkeland]

I would bet it's a bit of interference from one of the electronic devices in close proximity. 

[Kitchener]

Yeah, I guess.
I’m going to be taking the Crack home for some mods in a week or two, might be interesting to see if the same sound pops up outside of the office.