I'm new to the TomTom ONe and I've notice that on occassion, I get a Gong Alarm sound and a strange icon will appear at the top left of the map: a white box with an EKG like symbol in it with numbers underneath- - 2.4 or 5.4 or 1.3, etc. Typically the numbers will fluctuate up and down. Then it will disappear altogether. I've tried the manual and google but can find no reference of this. You guys are my last resort. Any ideas????