Found this on a RC groups forum. One think it suggests is if you plug in a new battery w/ out turning of the transmitter, it will cause this problem. It does say that it was only the light blinking; however since it was posted in 2009, newer firmware could have added the sound. Will still put in new batteries.
There have been far too many posts about this condition, so here is the answer. The blinking LED was put into the latest firmware as a tool to help you diagnose a certain problem. It is there to tell you that the receiver rebooted during operation (flight). The intent was that you would look at the LED before you launch to notice that it was solid, then look at it again when it came back. If it was flashing you knew you had some kind of power supply fault.
The side effect is that the LED will also flash under a few other conditions.
What happens is the receiver remembers the 2 "channels" that it was using when it last had power. If that matches with the two channels that it now finds the transmitter on, it will flash thinking it had a power outage. Under certain conditions this could happen after days of sitting at home waiting for the next flying day because the transmitter may start transmitting on exactly the same channels as the previous day (slim but not impossible). Also if you land and change batteries without turning the TX off, the receiver will power up and find the TX on the channels in memory and think again that it had a power outage (which it did since you just changed the battery).
How do you avoid this when you are just changing the battery? Turn the TX off before putting the new battery in the model. Yes this will power up the receiver first which many have been taught is a very bad thing to do, just turning the TX off and back on while the receiver is powered down may be enough to allow for a channel change (but I found this doesn't always work with the LP5DSM TX). The only sure fire way is to connect the receiver first, then wait more than 2 seconds for it to start scanning for the TX, then power up the TX.