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.