Humming when connected in stereo

Hey y´all . I recently got 2 Presonus Eris E5 studio monitors, when i got the first one i plugged it with no problem to the QC output 3 for mono output, barely a small hiss associated to the guitar, when volume was down there was no noise.
Then i got the second monitor and when i plug both the output 3 and 4 it´s a massive buzzing/hissing sound even with the guitar down
I´ve tested both monitors in each output by themselves and the issue only arises when they are both connected. They are connected through the same 1/4 " plugs as i use for guitar.

So:
Monitor 1 to output 3 with cable 1 works fine
Monitor 1 to output 4 with cable 1 works fine
Monitor 1 to output 3 with cable 2 works fine
Monitor 1 to output 4 with cable 2 works fine

Monitor 2 to output 3 with cable 1 works fine
Monitor 2 to output 4 with cable 1 works fine
Monitor 2 to output 3 with cable 2 works fine
Monitor 2 to output 4 with cable 2 works fine

only when they are both connected regardless of output, cable, etc theres this loud hum, my guess it´s something to do with the having a grounding issue when connecting both speakers

what do you guys think?
has anyone dealt with this?

Have you tried the Ground Lifts?
Is everything plugged into the same outlet?

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they are plugged to different outlets, not sure how to ground lift tho

Sounds like you’re creating a ground loop.
Try the ground lifts, they’re found in the swipe-down I/O menu

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oh man but the outputs 3 and 4 have no ground lift option, maybe if i try with xlr cables i guess

Are you using TS or TRS cables? Definitely sounds like a ground loop

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try the Input ground lift, just in case

ts cables, haven´t tried trs cables but would that fix it?

tried it but didn´t change it

i don´t have trs cables and im trying not to buy more stuff unless it could be a fixing issue hehe

TRS are for balancing the signal, or you can get a ‘humbuster’ version (if you’re willing to use Send1 or 2), that could indeed mitigate the noise problem, but it’s hard to guarantee. That was going to be my next suggestion, other than plugging everything into the same outlet if possible

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in the sends i can just use them as outputs or do i need to do something different? im gonna look for some trs cables and see if that fixes it first thoug
thank you so much

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they’re good to go as Outputs- just need to connect them and change your Output Block to correspond to the send you use
Screenshot 2024-01-26 143147

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HELLO EVERYONE THE TRS CABLES FIXED IT i am dumb and have no job in electronics so i didn´t know the balanced cables would fix it, thank you all again for your disposition and help!!! love you

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Fantastic! That’s what we like to hear

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