If the mountain range is not large enough or high enough it will not have silver in it. Silver is usually at and above the elevation you find obsidian. Start at the very top and search there first.

Regarding the tempo of the beep you want it is about 105 to 107 beats per minute. I alt-tab out and use a online metronome set to 106. When the game and metronome are in sync you are right on top of it. Happy hunting!