GM-GMC: 91 chevy x-cab truck, electric fuel pump, power doors

Question
truck makes a cliclking sound when key in "on" for about 10-15 sec.then stops...and agian when you cut truck off.. and key in your hand..sounds like electric pulus????? cant pin pointwhere from...sounds like passener side..at heater core???     91 chevy x cab, bought it used w/ new 350 engine, auto trans, power doors and locks.. thank you for any help...
            ken

Answer
I believe that you may be hearing either the heater blower motor or maybe some sounds from the electric fuel pump.

If the truck starts and drives well, I would not worry about it.

If it is the blower motor, it will get worse until you have to replace the motor.  If it is the fuel system, some noise is normal durin operation of the vehicle.