1997 Oldsmobile Bravada

When I hit the gas and reach about 20 mph this noise starts that sounds like a cricket. It is geting louder and louder. If I let off the gas the noise goes away but as soon as I hit the gas it starts agin. The noise only happond when I hit the and the truck has to be moving. The will not happond just by reving the engine up. The noise sometimes happonds when I hit the breaks too. I wastold it was a speedometer cable but I was also told that the 1997 does not have a speedometer cable.