Mitigate harmonic interference

Hi Experts.

I have found harmonic interference.
I have guys doing interference hunting inside the place, because we have interference on indoor site.

Any suggestions to mitigate?

Is it reflected in OSS counters?

Yes it is.

Which band is this exactly?
Using in which technology?
There must be any device in place whose noise is in this rangeā€¦

It is 900 band.