The pad switch on a condenser microphone is designed to prevent the microphone from being overloaded by very high sound pressure levels. It does this by making the input to the microphone's circuitry less sensitive.
When you use the pad switch, the signal level going in to the circuitry from the capsule is reduced by 10 dB (or whatever), but the inherent noise level of the circuitry remains unchanged. So the pad switch makes the microphone 10 dB (or whatever) noisier relative to the signal, and 10 dB more vulnerable to interference as well. Furthermore, the pad switches in many microphones indirectly cause increased distortion.
In short, the pad switch is for emergencies only, and should not be used unless the microphone is in real danger of overload due to extremely high (generally for modern microphones, humanly intolerable) SPLs.
It sounds as if your microphones aren't in any danger of overload, but their output levels are too "hot" for the inputs of your preamp or recorder. If so, you need resistive pads at the inputs of your preamp or recorder (on the far end of the cables away from the microphones). They preserve the signal-to-noise ratio of your setup, since they reduce the inherent noise of the microphones by the same amount as the useful signals. Meanwhile, signals in the cables (up to the inputs of the pads) remain at the higher level, so any interference that's present will have that much less effect on the recording. A 10 dB (or greater) reduction in interference makes a very welcome difference!
You can get high-quality, relatively inexpensive balanced resistive pads (built into XLR barrels) from many sources. I recommend the ones made by Shure; I've measured quite a few of them and I know that their balance is very good; that's important in keeping interference to a minimum. Other brands may be equally good but I haven't measured them, so I don't know for certain. -- These pads are purely resistive, and phantom power passes through them with generally negligable effect.
Of course, some recorders have switchable input attenuation built in, or a "low/high sensitivity" switch of some kind. If that's available, it's usually a good alternative.
--best regards