Now, I looked under the crack and noticed one of the red LEDs is off. I took voltage measurements per the manual and found Terminal 1 (and everything connected to it) was showing like 160V. That seems a bit high.
If terminal 1 is that high, either 7 or 9 will also be really high.
Look at the 12AU7, do you see glowing dots on both of the internal triodes of hte 12AU7? If not, the solder joint on A4/A5 is not doing its job.
I suspect that the noise you're getting could be normal, but you're getting it on the working channel but not on the channel which isn't conducting.
(BTW, does this Crack have a Speedball?)