Re: radio interference
FM is not noise free, but less sensitive to noise than for example AM. When the signal strength goes under a certain level the noise comes very fast because the FM demodulator has not linear signal-to-noise characteristics.
The reason you hear noise in certain places can be:
1. The signal strength is to low.
2. The signal has multi path propagation (and adds at your antenna out of phase)
3. High noise level (from for example electrical equipment, electronics, computer etc)