UD-ULTC4K Displaylink Causing Pulsating Static in Studio Monitor Speakers

I’ve looked around the internet quite a bit and found a couple topics on this forum that have popped up around this exact same issue, but never resolved. So, I thought I would resurrect it.


I have the Plugable UD-ULTC4K that is hooked up to a 2019 Mac Book Pro via Thunderbolt 3 cable. The video monitors work flawlessly, but the problem is I’m getting this pulsating static from my studio monitor speakers that are connected to an Apollo Solo audio interface via 1/4" TRS cables through a separate TB3 port.

I suspect this is primarily a dock issue, because I’ve isolated the Interface, speakers, and all line cables approximately 5 feet from any computer wire or peripheral. I’ve unplugged all external peripherals and video monitors from the dock and left only the main TB3 cable plugged into the laptop and the static is still audible. I’ve also swapped out cables, both TRS and USB-C, switched around to different TB3 ports, plugged the speaker power cables into separate outlets from the dock, and nothing outside of complete disconnection has had any effect.

The static 100% dissipates ONLY when I fully disconnect the dock from my Mac Book Pro and use the laptop screen.

The static is rhythmic to the point where you could put a metronome to it, almost like the ticking of a second hand on a clock. I’m guessing possible processor feedback? And it has a lower frequency buzz whenever I scroll a page, hover my mouse pointer over a button, or any other movement/input via mouse or keyboard (both are bluetooth, if that matters). Turning off the bluetooth doesn’t alleviate any of the issues, in case you’re wondering. Neither does cycling the power on the dock itself.

Is there some kind of fix or suggested work around to alleviate this annoying static? It’s happening only through the speakers, and not through my monitor headphones.

Hello Rich,

Thank you for contacting Plugable support! Sorry to hear about this issue. I’d be more than happy to assist you.

Are you familiar with a ground lift? https://www.wikiwand.com/en/Ground_lift_plug

I’d recommend to isolate the dock (or your studio monitors if they are powered) from the ground using one and see if that stops this interference. Usually noises from devices like our dock are passed through the common ground.

As an example, I have a headphone tube amplifier that I use in my home office. It will pick up noises through the ground from my desktop PC. To eliminate this issue, I use a ground lift on my tube amp (as I prefer to keep my PC grounded). For your situation, isolating the dock is probably best since you may want to keep a common ground between your other audio equipment. But you can experiment and see if it’s more effective on one device vs the other.

Please don’t hesitate to let us know of other questions.

Thanks again for contacting Plugable support and best wishes!

Joshua Henry

Senior Engineer | Product Owner
Plugable Technologies

Yes, I’m familiar with cheater plugs. I’m also familiar with how unsafe they are. I’m actually a little surprised that’s a recommended fix, given the potential fire hazard and other safety issues. They’re even mostly illegal in Canada.

Would something like this work (and be safer)?

For what it’s worth, most our devices (like this UD-ULTC4K) are designed to be used in multiple countries worldwide, like Japan for example, which has no ground connection on their AC plugs. So it isn’t all that unsafe to connect our dock via one in this specific context. However, if a ground lift is illegal in Canada, then I suppose you’ll need to comply with local regulation. These plugs are quite commonly found here in the United States at any local hardware store.

I have no experience with that specific device I’m afraid. It will depend upon what frequencies and how they are being filtered out.

Best wishes,

To clarify, I’m not in Canada. I just don’t want to risk electrical shock or potential fire hazard in my home. You can simply Google “Are Cheater Plugs Safe” and I’d say 99% of the articles that populate will tell you how safe they are. Just because they’re sold in the States, doesn’t mean they’re a safe solution.

From wikipedia:
In the professional audio and video fields, the cheater plug has been identified as a serious safety problem. Its casual use as a method for avoiding ground loops in analog audio and video signals (to eliminate hums and buzzes) is dangerous. Bill Whitlock, president of Jensen Transformers, writes, “never, ever use devices such as 3 to 2-prong AC plug adapters, a.k.a. ‘ground lifters’, to solve a noise problem!” LINK

But that’s not the issue I’m here to discuss.

I do want to update that I just tried plugging the dock into an outlet on a different breaker circuit and the static has completely vanished. So it is in fact a ground loop issue. I’ll move forward with the HUM X and update if this topic isn’t closed before then.

Thank you for your help in solving this issue, Joshua.

Just checking in to see if the HUM X worked out for you? If it’s not arrived yet no worries.

Thanks and best wishes,

Hey Joshua, I wanted to do a bit of testing of different solutions before I responded.

Turns out, it was definitely a ground loop problem with the DisplayLink 4K Hub pumping unwanted noise into the wires. I tried the Ebtech HUM-X and Pyle PHE-400 Mini HUM Eliminator and both solutions removed 100% of the static interference.

For the HUM-X, I purchased 2 units, one for each of my KRK monitor speakers. Everything is living on the same surge protector and no additional wires were added to my setup. A super clean and easy fix that still allows safe grounding of the speakers while eliminating any ground loop static.

I also tried the Pyle PHE-400 Mini Hum Eliminator. I plugged the TRS cables from my monitor speakers into Channel 1 and 2 OUT, and purchased an additional shorter set of balanced TRS cables for the Channel 1 and 2 IN to my Apollo Solo DAC. Though this solution was a BIT cheaper (about half the price including new cables), it added a TON of additional cable rat nesting to my already wire-ladened work station.

Either method should work great for this type of issue. I’m happy with both results, but definitely prefer the cleaner solution of the HUM-X. I also have this set up with a Razer Chroma eGPU and it is the same solution it needed.

I really hope this topic helps anyone in the future experiencing this same craze-inducing static issue with hubs and eGPUs.

  • Rich
1 Like

That’s fabulous news! Thanks for sharing your solutions and testing performed. It’s most appreciated, and I’m sure others who encounter this issue will find the information useful if not comfortable with the ground lift/cheater plug method as originally suggested.


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