Honestly, these sorts of issues are hard to troubleshoot, short of replacing a bunch of components.  Sometimes you might get lucky after moving a few things around.  However, I can give you some feedback from personal experience.
 
I was used to running the original NU Audio card between my SLI graphics cards, but the watercooling fittings were a bit too low to allow the height of the NU Audio Pro to set there.  I tested a USB riser cable (PCIe x1 -> USB3.0 -> PCIe x16 slot powered with a 4pin Molex), which I've used with a couple other audio cards in the past.  Results were less than...expected.  I didn't get extra noise, but ran into some serious latency issues; some would occur after going to sleep, while others would start after opening enough browser tabs.  Also, game performance dropped significantly and it seemed like games ran extremely choppy - a hallmark of some really bad latency.
 
Side note - It is entirely possible that there were a couple different driver issues going on, as my latency was caused by either the Audio drivers or the default Storport drivers from Microsoft (I have several RAIDs and over a dozen HDDs/SSDs).  This could have been caused by moving around power connectors, which were needed to power the PCIe riser slot and HDDs, or moving the Audio card to different PCIe slots.  This persisted after I swapped over to the riser I'll mention in a second.  Ultimately, it took uninstalling/reinstalling the NU Audio Pro drivers, NVIDIA GeForce drivers, Intel Chipset drivers, and uninstalling the IRST drivers and installing the new Intel Optane and Storage Management software via Windows Store.  After that, everything worked fine and I've not run into an audio issue since.
 
I got one of these:  https://www.amazon.com/gp/product/B07PMQZ1HP/, and it both works and works well.  If you want to give a riser a shot, go for it.  I would only expect issues to still occur if the electrical noise is being passed through the motherboard.  I'm not sure a riser would help block that.

Without a large sample size to test, of course, I'd try to stay away from USB connected riser cards (too many USB buses in a row, possibly).  Then again, it's possible that this had nothing to do with my issues I mentioned above.
 
I'll run the noise issue by our friends in Audio Note to see if there's any commonality between those two ports.  Unlikely, since one's at the top of the card, and one's at the bottom of the card.

Hey, I have finally run the tests. I can now say that my electric noise problem is an issue with the Ground loop. However, riser cards are also perfectly fine you you have no free PCI-E for additional Pro card or its placement is bad.
I have connected the riser to 6pin power only, I have NOT used the PCI-E slot and the PCI-E to USB card for the riser. This way, the Pro card (the 2nd one in the pack, used for surround only) is connected by the special DP cable to the main card and is connected to riser card for power only (no data connections). It works like a charm. If you need space for placement - feel free to use.
 
It did nothing for the noise issue, so, its not about PCI-E power noise, I can be sure.