I've dealt with a bit of interference issues with USB + 2.4 GHz signals, and, to me, this sounds like that. In many cases, changing the WiFi channel dramatically improves this specific type of WiFi issue (many people never configure the router to the optimal channel!), and switching the router frequency from 2.4 GHz to 5 GHz eliminates it (the processor is unrelated to the WiFi signal frequency.) This issue seems somewhat more common when a signal has to travel more distance and especially through several walls/floors, is surrounded by other 2.4 GHz signals (clutter), is using a channel that is not considered optimal by the Mac, has to contend with lower quality cables with inferior shielding, is exposed to other multiple sources that also can cause or worsen interference, and it appears to be more noticeable with some routers than with others.
There's no way for me to say this is for certain, though. But, if you change the Wifi channel, change to a 5 GHz signal, try a different router, or buy a different cable for your hard drive, and one of these solutions makes a difference, it's a pretty sure bet that this is WiFi interference.
If you change your router to 5 GHz, the issue should disappear entirely because the USB interference is confined to within the 2.4 GHz band -- if you change to 5 GHz and this signal persists, then it is most likely not being caused by USB interference.
It's more of a byproduct of USB than it is a design failure. In many cases, Users can reduce or eliminate the problem, and the many benefits of USB outweighs the drawbacks like this, in my opinion. Further, if the USB device or a low quality cable is the culprit, there's no way for any computer Maker to prevent this.
If this is an interference issue, a replacement probably will not resolve the problem. Changing the router to 5 GHz is probably the fastest way to test this out. Do note that 5 GHz is not as good at penetrating barriers, so, if you switch to 5 GHz and this fixes the issue, you may still need to use 2.4 GHz (depending on router placement) - and so you may want to then explore some of the other options that will reduce such interference while still allowing you to use 2.4 GHz.
Also, are you using USB-IF certified cables? (cheaper cables not built to USB specification can have inferior shielding, which can cause interference issues or make existing inference issues worse.)
Here is some documentation
https://support.apple.com/en-us/HT201542
https://www-ssl.intel.com/content/w...al-bus/usb3-frequency-interference-paper.html
[doublepost=1489540834][/doublepost]Have you ever performed the WiFi scan to get the specifics on channel, frequency, noise level, etc?
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