Buzzing sound

Hi ppl!

Today I bought a Sub for my monitors which could’nt cover certain frequencies.
After installing it I noticed when thers no output I get a subtle buzz from both speakers which was not there before installing the Sub.

i have to mention I use XLR-> TRS from monitors to sub and TRS to TRS from sub to interface.

It doesn’t bother me but i’m concerned if this situation is doing any harm to my setup.
What’s your thoughts,

peace

LE:
the speakers are presouns eris e5 and the sub presonus sub8

any wall wart/power packs? they can be a source of hum.
otherwise, could be ground loop hum.

Problem solved!

I had the 5m long TRS cables hanging loose in the proximity of the power strip.