I have had a similar noise emanating from either the left or right channel when a tube begins to act up. But this noise is more of a rush, less of a rustling cracking noise with occasional ticks and pops. although both are about the same low volume. Of course, this noise is only heard when no music is playing. If you swap tubes, however, and the noise moves to the other channel, the problem is in the tube. Then you put in NOS tubes.
Yet, if you swap tubes and the noise remains in the same one channel, the problem is in a component(s) on that channel in the circuit board. If your tech pulls the tube, and the noise is still there on his oscilloscope, look elsewhere, down stream of the amplifying tube. If, as in my case, the C1 upgrade was performed, a capacitor or two on the offending channel can be pulled to pin point the offending component part.
In my case, an issue that I asked CJ twice to sort out and they did/could not was found by a local tech with considerable experience, particularly with studio and music equipment. The problem, one I endured for 10 years, on this PV15 was in one MOSFET, where there are two, one for each channel. I don’t know the technical stuff, but he said that MOSFETs can be damaged by current and this almost always will compromise the part.
In my case, he showed me exactly what was going amiss. Once compromised, the channel will always be noisy, even if the unit specs out to CJ unit values. Typically, when a capacitor is bad, it has noises such as this, but often after the component warms up, it will pop, then play fine for the listening session. If that capacitor is in the power supply, maybe that is not the case.
The tech I used replaced the two MOSFETs with matched pairs (and he ordered 8 to sort them), and the PV15 works brilliantly. But that was my problem, not a capacitor issue in the power supply. The MOSFETs he installed are 400v MOSFETs. One thing to keep in mind, I’ve been led to believe that MOSFETs are notorious for being noisy at high frequencies, about 25% of stock. So some care is required to ensure two good ones are employed.
I must of spent four hours on several separate occasions on the internet searching "Conrad Johnson noisy channel" and spoke to a number of techs, including CJ (several times) about this. Before the local tech fixed the issue, I wrote to CJ for the third time ( including having them physically look at the machine twice). Their current service manager told me he could fix the machine, and he rightly knew it was not a capacitor issue. Then he dropped a bomb: the minimum charge was three hours, $396. To me the message was clear enough, "We really don’t want to help you and we are not going to stand behind the earlier CJ work or promises." I hate to be so harsh but that was one of the most disappointing emails CJ could have sent me, particularly since I own other CJ components.
I got the PV15 fixed for $70, parts included. The unit works brilliantly now.
This write up is provided to detail my case for one reason only. To help other folks fix their machines and not waste the time I did. So, if other folks have a noisy channel on a CJ preamp/linestage of this vintage, and it is not a tube problem, look to the MOSFETs as one possible issue.