It could be that you need coolant or it's low.
Would depend on what year impala On a 63 impala or many of the early ones you need to remove the passener side fender. The remove the power wire from the blower motor. Then remove the heater hoses. then remove the heater box from the fire wall. the heater core is inside that box. Newer models I am not familiar with
A 1974 Chevy Impala frame would work
ON the 2006 impala that whining noise is actually the electronics when you accelerate. Its more or less electronic pulses/signals My 06 Impala is the same.
Thermostat.
It could be a weak battery or a bad ignition coil.
Your heater relay switch may be bad
Check fuse if the blower is not working. If it is then replace your heater core. if its not then replace your fan switch.
Bad heater core.
Check with your local Chevy dealer on that.
no
Leak in heater core
intake gasket, leaking radiator and radiator cap, leaking heater core,, air in the sytem that needs to be bleed by the bleed screws,,,but most of all on all these cars with the 3.8 or 3.4 are bad about intake gaskets,,hope this helps