I was having a hideous high pitched sound when connecting two different cases together using Hermod.
It took me a minute to track down the problem, and it turned out to be the stock power supply which ships with the Intellijel 4U cases.
15v - 4A - 60W
When I disconnect from the main case, the noise was gone.
I posted a series to Instagram about this:
https:// www. instagram. com/p/BiaXjcRAJsc/
I corrected this swapping the GSM60A with a second PSU
15V - 6A - 90W
I happened to have a second for the main case around because of the grounding issues with a René which needed a different grounding scheme. When I use the GSM90 with both the main case and the 4U case the noise is completely gone (as shown in the instagram series.)
I’m relieved that for me it didn’t turn out to be the Hermod at all.