Hi Manganos,
Welcome, I am a newby here too. Relax, I did that too. I still Have the MXT.
If you ran your MXT for any length of time you would know that you could sit in the living room while watching the boob-tube and air-test to your hearts content. I watched 2001 a Space Odyssey about five times getting to know mine and making some notes. I had three coils. Then I tried the tests after turning the machine on.
I cannot do that with the F75. The fact that it can receive any noise does not mean it receives all noise. It is a sensitive receiver. You will find that it will hunt and ID when it is swamped with noise where and when you encounter it.
If you had a filter or noise cancelling feature it might not perform the same. The only place I recall I ran into noise was in the house, but I am wondering about the cell phone because it makes noise on radios and audio stuff. Remember that the first time out.
I did the same thing and had to go outside away from noise sources in the house. First time I tried it out, I was in the house and I knew better as soon as it started to report. To me that is a good thing because most of my detecting is outside. You can turn down the sensitivity and find the noise sources. The SunRay FX-1 probe if I recall is quieter indoors. Why? The F75 stock coil is part of a selective receiver that is sensitive and in some gear that takes a bit more design and build than the lesser products. The nature of the probe is in how it is made and of what. The probe is more selective to noise because it receives the electromagnetic portion of the source signal as opposed to the electrostatic portion. The two, Electromagnetic and Electrostatic waves are 90 degrees out of phase. The probe is a ferrite core antenna like those found on an AM radio and are less susceptible to electrostatic noise like those from lightning. The stock coil though a magnetic loop in comparison is more susceptible to electrostatic sources even if they meet FCC standards for noise emission. You have a sensitive machine that can hear more signals that are noise, so what do you think it will do for receiving it's own reflected emissions from targets? It makes 'hunted out' areas all new.
Not every situation allows me to detect at full sensitivity, but most do.
Sounds like it is working normal and that dog is ready to hunt.
You are gonna love the F75!
Sunny Jim