Our "new" 2010 RX is our second Lexus with fobs & push-button start. When I push the start button to start the engine, I first hear a one-second "BZZT" noise from behind the instrument cluster, then the engine starts. This happens every time I start the engine, but I've never heard a noise like that in our 2008 ES350. So I wonder if this is normal? Does anyone else hear this odd buzz noise just before your engine fires up?

 

Our 2010 Rx 350 does not make this noise.

 

my 2011 does make that noise. I think its from the fan or motor that cools down the nav screen

 

Hmmm. Not sure that's it since we don't have NAV in our RX.

 

hah, then I really don't know. But I know its like two short bzzzz sounds about two seconds after you have pushed the start button

 

Sounds like a relay coil/contacts chattering. Not present on our RX but present on our Accord.
No real worries other than the minor noise.
Might be an easy fix if you knew just where the relay was & could reach it without too much dis-assembly. My bet it's a <$25.00 part.
Coil needs a solid 12V to pull the contacts in, works just like an electric solenoid.
Pitted contacts will cause chatter, dirt/dust between the contacts will cause chatter, low voltage <12V may also cause the chatter.
What condition is your battery in ?? Original to the car ??

 

Yeah, that's what it sounds like.

Battery appears original, but the RX spent the first 3 years in Arizona, & that heat can trash a battery quicker than cold.