ORIGINAL: BasinBum
The most common noise on 72 at our field has been what sounds like broadcast television audio which has shown up on various channels for about ten minutes at a time. After a PCM lockout occured (while flying on 72 and luckily went away withing about 20 feet of the ground) I switched on to hear the same noise.
Check with a FM radio when you hear the noise on the scanner and see if the noise is a FM radio station. Even if the noise is hard to make out, listen to it with one ear while tuning the band on the FM radio for FM stations. When you match it it will be very apparent.
We have a FM tower about a mile away and I get it on two scanners (Icom ICR3 and Rad Shack Pro-26) on both 72 and 52 MHz. This tower has two FM stations on it at 104.5 and 105.5 MHz. It's the 105.5 one that I receive and I have been unable to pin point if it is a problem. Last Thursday the station was there in the morning but the noise went away at about 11 AM? I made contact last week with the station and am waiting a call from their engineer.