Unknown noise after driving car 15 feet...Transmission? Or???

[imnprsd]

After I drive my 97 Blazer 15 feet (forward or reverse) I hear a funny sound... Almost like a release valve purging or something to that affect, but it's more mechanical in tone vs air purging. Any ideas? I have 115K miles on the car and it looks like it's been properly serviced.

Note: I also once owned a 95 GMC Jimmy with 95K miles and it did the same thing, but not as loud. What am I hearing?

[ricksza]

Check your owner's manual under Brakes, Anti-Lock. I think the noise that you are hearing is the self test.

[Mikado14]

At approximately 8 mph, it will do this.