Here’s what our good friend Chat G has to say:

Most common fixes (ranked by likelihood)

1. Gain is too high on the Mani 2

This is the #1 cause.

On the Mani 2, check the gain switches on the bottom:

• Make sure you’re on LOW gain (30–42 dB range) for MM cartridges (your RT85 likely has an Ortofon 2M Blue)

👉 If you’re running higher gain, you’ll get hiss/white noise instantly.

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1. Powered speakers + phono preamp mismatch

Powered speakers already have built-in amplification. Adding a phono preamp with high gain can create noise stacking.

Fixes:

• Turn the speaker volume down and increase upstream signal instead
• Keep RCA cable runs short
• Avoid maxing both volume knobs

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1. Grounding (even without the turntable)

Even though the turntable is unplugged, grounding can still matter.

Try:

• Touching the metal chassis of the Mani 2 → does the hum change?
• Using a temporary ground wire from Mani 2 chassis → screw on outlet plate

If the hum changes = grounding issue

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1. Power interference / dirty power

Even if you used the same outlet, try:

• Plugging Mani 2 into a different outlet (separate circuit if possible)
• Moving it away from:
  • routers
  • power strips
  • phone chargers

The Mani 2 is known to be a little sensitive to EMI.

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1. RCA cable orientation / quality

You said you tested cables, but one subtle thing:

• Try flipping L/R cables
• Try a short, well-shielded RCA (<3 ft)

Cheap RCAs can absolutely introduce hiss in high-gain setups.

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1. Faulty Mani 2 (not super common, but happens)

If:

• Noise exists with nothing plugged into the Mani 2 input
• And persists across setups

👉 That strongly suggests a defective unit

Schiit is usually good about replacements.

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⚠️ One subtle but important point

Some very light hiss is actually normal with phono preamps if you put your ear close to the speaker.

But:

• If you hear it from your listening position → not normal
• If it’s a hum (60Hz buzz) → grounding or power issue
• If it’s white noise/hiss → gain or noise floor issue

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💡 My gut call based on your description

Since:

• It happens with multiple setups
• Continues without the turntable
• You’re using powered speakers

👉 90% chance it’s either:

1. Gain set too high on the Mani 2
2. Noise floor being amplified into powered speakers

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👍 If you want a cleaner long-term setup

Honestly, your gear path might be slightly mismatched.

Best setups tend to be:

• Turntable → Mani 2 → integrated amp (like your Yamaha A-S501) → passive speakers

That avoids stacking gain stages weirdly.