Line Inputs and Excessive Noise

I’ve got an amplified microphone plugged into the line in, but it gives loads of noise; a low hum that is louder than most other sounds. I tried a ground loop isolator with no luck and a different microphone/preamp. Any ideas how I can rectify this?

My dear friend

Maybe your microphone has too much gain.
You can try to turn it down, or you can use a passive microphone

have a good day

When I say amplified, I mean a powered pre-amp on a microphone, rather than a passive device. I have two sold as CCTV microphones and one good microphone connected to a preamp board.

I’ve tried all 3 different microphones each with their 3 different pre-amps, none of which are adjustable and all are sold as line level output devices. I have just tried two with a different stereo and both emit a small hum with that too. There must be something with those preamps or the power supply I am using for them.

I tried a passive microphone last year and started a thread about it last year, but there was no outcome from that. This is why I’ve bought some pre-amps.