I have a Trailblazer 2008, while driving usually highway (55 to 65 mph) I hear a series of 3 beeps and then after approx 1 mile it beeps three times again. this repeats for a while then stops, and then starts again. Nothing its lighted on the dashboard. I took it to the dealer but they were not able to diagnose the problem as it didn't sound when they tested it. This issue doesn't occur all the time so it has been driving me nuts trying to figure this out. Any ideas anyone?

 

question for you....
have you had your dash cluster exchanged for repair or something?
I have read of another Trailblazer that had a cluster exchanged...
the new one caused a tone or beeping when the vehicle reached 55 or some special speed.
I believe this is a feature on some export Trailblazers.

Another thing that makes the vehicle beep.... the parking brake being set....
so its possible that it momentarily thinks its set....

another thing--- turn signals on for more than 3/4 mile will set off a series of beep to let you know to turn off your blinker.

 

It should still be under warranty, why dont you take it in to be looked at?