I know that you use the radio to get rid of Snorlax infront of D Cave, BUT HOW?
You go up to the Snorlax and press A, In FR/LG.In HG/SS you'll have to turn on your radio. Then press A. Snorlax should wake up. Then you'll battle. In HG/SS Snorlax is level 50. In FR/LG Snorlax is level 50, too. (I think)
Source: Personal Experience
Info on PokeFlute: http://bulbapedia.bulbagarden.net/wiki/Poké_Flute
Dr. Flame is wrong. You need to open the radio to where all the channels are. Move the circle thingy to the top, on the middle. The Poke Flute should sound. Then talk to Snorlax.