Small problem with the UI24R

Lifespan

We've got a small problem with the UI24R which we use mostly only for In Ear monitoring;; it's built in in a rack and directly above it we've installed 3 Behringer ULRTALINK MS800 units so we can split the incoming channels, one signal to the UI24R for IEW monitoring and the other signal to the available FOH mixer. The Ultralink units each have 8 inputs so we have 3 of it. First numbered 1-8, second numbered 9-16 and third numbered 17-20. The third one is directly above the UI24R, and very strange, we'l have 'hum' on input 17 which is the most left input. Of course we tested all cords, they ere al ok; than we removed the unit form it's place; hum was gone; we changed unit 3 with unit two, so input number 0 was now most left input, and guess what; hum1 We changed the racks a little bit so now we have 1U room between the Ultralink units and the UI245R. Although it's a lot less, there still is some hum. We cvabn solve it partly by good use of the gate on this channel, but we think ithis is very strange. Does anyone recognize this problem???? And if so, know how to solve this??

TAICHEE

What's the input number 0 ? Perhaps 9?
So the CH9 has the hum noise now. you mean?

Anyway, noise issues are not simple.
It depends on the powe of the place, situations, something as well.

You have to try to detect the reason of that and it will spend long time.
Check the ground connection with the case and cable's shield and pin1.
Even if the cable tester told good, shield requires in pin 1 it is .
And it should be dropped to the metal case.
And also the ground would be better to dropped to the ground line of that building at one point.
If the ground-loop is there, break it. Cut the ground in the loop.

Anyway, nobody can works for the issue in remote.