What people call microphone noise may not be the fault of the microphone. There are three main sources of noise when using a microphone:
1.) Background noise in the environment, such as sounds made by air conditioners, road noise, or the coughing of an audience.
2.) Noise inherent in the preamp that the microphone connects to. All electronics add noise; cheap microphone preamps noticeably so.
3.) The self noise of the microphone.
Sound levels, including noise, are measured in decibels of sound pressure level (dB SPL), such that 1 Pascal of sound pressure is about 94 dB SPL. The quietest sound that can be heard is about 0 db SPL, a quiet room you record in might be about 35 dB SPL, a TV at normal volume might be about 70 dB SPL, and so on.
A condenser microphone specification typically lists how noisy the microphone is an equivalent db SPL level. So, for instance, a microphone with a noise rating of 16 db SPL is quieter than one with a noise rating of 25 dB SPL, but even 25 dB SPL is quiet enough so that its noise would hardly be noticeable when recording in a room with an ambient noise level of 35 dB SPL.
Sometimes a condenser mike will list the signal-to-noise ratio in dB instead of the noise level in dB SPL. But, you can then calculate the microphone's noise level in dB SPL as (94 -- the signal-to-noise ratio in dB).
Dynamic microphones generally don't include a noise spec because their self noise only depends on their impedance and their temperature. It will be lower than the noise produced by the microphone's preamp. For what it's worth, lower impedences (and lower temperatures) produce less noise, and the noise contribution of a dynamic microphone's preamp will be greater than the self noise of the mic.
The noise contributed by the microphone's preamp is specified in a different way than microphones, in units that equate to voltages instead of sound pressures. It takes some calculations to do the conversion to dB SPL based on a particular microphone's sensitivity. (For more details, research selecting microphone preamps range.)
In general, solid-state microphone preamps can be less noisy than tube-based designs, but in any event cheap consumer electronics have poor microphone preamps. So, a noisy microphone preamp may be the source of the "microphone noise" you've been hearing.