Icon Audio HP8 MKII: annoying noise coming from PC captured by left channel RCA input

[DeBilbao]

I'm really satisfied with my Icon Audio HP8 MKII headphone amplifier, but I'm experience a weird problem that is driving me crazy.

Until recently, I've been using different solid state headphone amplifiers and have been a great Burson Audio fan, but even the Burson Conductor can compare with the musical experience I'm getting from this great tube amplifier. My current setup includes two Shu Guang CV181-Z 50 Years Treasures drive tubes and one PSvane 12AX7 preamp tube.
 

 
 
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But I'm having a problem that's driving me nuts. The HP8 MKII is "capturing" noise from my desktop Windows 8.1 Pro PC through the left channel RCA input. It's not a continuous hiss but instead is some kind of sizzling noise.

My current audio route is the following: Windows PC Windows > Audioquest Pearl USB A-B cable > iFi iDSD micro > 2x RCA Audioquest G-Snake cable > Icon Audio HP8 MK II > Sennheiser HD 650 and I've made the following tests:
 

1. Disconnecting the left channel RCA cable, noise dissapears.
2. Rotating the left channel RCA cable conector, noise changes and there's a point where it is less noticeable but I want it out.
3. Interchanging left and right RCA cables or crossing them, noise persists.
4. Reversing the direction of the RCA cables, noise persists.
5. Changing the RCA cables with another Wireworld Solstice pair I have, noise persists.
6. Unplugging the USB cable from the PC and plugging it to a MacBook, noise is still present if the PC is turned on.
7. Shutting down the PC, noise persists.
8. Using another source component via RCA input, noise dissapears.
9. Connecting the headphones to the iFi iDSD micro as an amplifier, and the noise is absolutely absent.

Any suggestions? I'm really close to sound heaven, but this noise is driving me crazy.
 

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[DeBilbao]

I'll share with you my advances on this annoying issue:

Yesterday night I performed a test that in my opinion offer a definitive diagnostic: noise is generated by my Windows PC and captured by the amplifier by some kind of induction.

The test couldn't be easier, power off and disconnect the iFi iDSD micro from the line input of the Icon Audio HP8 MKII amplifier and connect to it my Denon DVD-2910 multiformat player. This is what I got:
 

1. With the PC turned on, noise is present.
2. With the PC turned off, absolute silence, even with the pot at 100%.

After this conclusive test, I performed another and took the Icon Audio HP8 MKII amplifier and the iFi iDSD micro DAC to another room in the house, but instead of connecting it to the Windows PC, I plugged the DAC to my MacBook with the same Audioquest Pearl USB A/B cable. This is what I got:
 

1. Absolute silence, even with the pot at 100%.

I must point out that I performed the same test yesterday, but with the MacBook in the same room than the Windows PC, and in this case I heard the noise.

So being the Windows PC the culprit, I tried opened it and tried to identify if any position change affected the noise, or if touching any cable using myself as a ground the noise was altered in any form. I also decided to deep clean the computer, removing every piece of dust with a vacuum cleaner and make a general revision of the cabling.

The result? I'm still experiencing noise, but at a much lower level. So low that at quarter of the pot I barerly notice it and this is the maximum SPL I can listen at with normal recordings. But if the passage is near silent and I try finding it, I can still identify it as a sound associated with the activity of the computer.

Another disconcerting news is the fact that now noise isn't associated to a single channel. If I disconnect the RCA cable either from the right or left channel, noise is present. A bit baffled with this change.

One more observation is that if I shutdown my Windows PC and put on my headphones with the pot at 100%, noise doesn't come out until the Windows logo appears on screen. During POST BIOS processing noise isn't audible. I've tried booting the computer from a Linux USB stick and noise is still present, so I discarded Windows as the faulty componente, but this also baffled me again.

It seems that only when hard drives begin with their activity noise appears, and the noise seem shaped with hard drive activity.

With this new discovering, I opened the computer again and started disconnecting the hard drives one at a time until only the system hard drive was present, but noise was present. I didn't try without the system hard drive or changing the SATA port because it's an SSD unit without mechanical parts.

Yesterday I was really tired and went no further. Tonight I'll try changing tubes in the amplifier and follow some of your advices. I'll keep you updated.

It's a long run but with your help I'm sure I'll fix it.

 

[java]

RCA cable with inadequate shielding?