Saturn SL 1 making some strange noise

Hi,
I just purchased a 1995 SL1. It has 95,000 on the car. It was a tow vehicle for an older man.
It has an automatic transmission. It runs great but makes this funny noise. When you put the car in drive after having it completely shut off and after starting to accelerate to about 5 mph it makes a funny click clack noise followed by a beep. It does not sound mechanical but like a relay or something. It only does it once. As long as you don’t turn the car off completely it does not do it again no matter if you put it back in park. If you turn the motor off and turn the key to ACC it does not do it. No other sounds at all. Transmission shifts fine.
Has anybody else ever had this problem or know what it might be?

Thanks
Fionnbharre

Try this site. These guys are Saturn fanatics.

http://www.saturnforum.com/forum/saturn-s-series-sedan-27/

It might be the ABS unit self-testing.