It is related to Toyota Link. It usually is only one beep on start up, to initiate the system during start up. If you have five or however many it is, it usually means that the system monitoring/tracking has been turned off. Since your car is an '07 build your subscription may have lapsed (3 years included from date of purchase), hence the monitoring would have been turned off, unless you have renewed your subscription. If you have no idea if your car is being monitored, just press and hold the Toyota Link button. If it rings, ask the person on the other end if your car is being monitored, and when your current subscription ends. If it doesn't ring that means you've been disconnected, and your subscription has ended. If you have no idea what Toyota Link is, and have never used it, don't bother renewing it, it is a $240 annual fee.