Atwood water heater "not sparking"

[Moonstruck]

I seem to have an intermittent fault. Yesterday I renewed the wiring of the atwood water heater on my '89 Excella. As soon as I threw the switch it fired up and started to heat the water. However, the gas was running out and I had to wait until today to get a fresh tank of gas. When I threw the switch a second time the heater just made a muted high pitched whine and then reset to the red light. Having had the heater running I checked the gas supply and had both the stove top and the Suburban furnace running perfectly. Any suggestions as to what might be causing the noise i'm getting? Marc