[kayliebug]

I just bought a 1998 Suburban and when you turn the key before it starts I hear a whining noise back by the gas tank ( I assume it is pumping gas because I have heard this noise on other vehicles).
The problem is that once the vehicle is started the noise is constant.
Does anyone know what it is. Also what should the gas mileage be in the city and highway.
I think it has a 40 gallon tank. Is this true.

Thanks for any help