I hate that too but you cant turn it off on my Tundra.
Just found this on a Tundra board. Posted by a member.
SWITCHING BEEP SOUND ON AND OFF
I just did it and I love my Tundra 110% now. Just in case there are copyright issues, I won't paste the text verbatum. However, here is my own words to describe how to disable this feature (mine are better anyways).
1) Unlock the Tundra
2) Open the Drivers door
3) Sit down (this took me a few tries and I got tired of leaning in)
4) Read the next steps before proceeding as they are all TIME dependant
5) Insert the key all the way into the ignition
6) Remove it Immediately
7) Reinsert the key and turn the ignition to ON [ahem... within 5 seconds of step 6]
8) Wait for the normal startup beeping to stop [bout 10 seconds]
9) Push the unlock button twice within 10 seconds. The Tundra should beep twice to confirm the programming change.
9.a) This didn't work for me as I tried it by the book (just 2 times). So... I just kept pressing the unlock button until the truck beeps 2 times confirming the change.
Hope this helps any others. Not sure if this will work in the pre '04 Tundras (or any others for that matter).