sometimes when I start my 6th xk and dhift to reverse I will hear a electronic solid beep. thought I shifted too soon and revs wrer high. on cold starts she revs about 1200 but she slows to 650 by the time I fasten my belt and lower the top. no error shows up. today, car was at 650, shifted into reverse and had the same beep. shift to park then back to reverse no beep as always. any ideas?

 

Sounds like the reverse warning senor (object too close to back of car) is giving a false signal. Either covered with dirt/debris or has water in it.

 

sounds right. won't worry about it for now.