[xtremewhite99]

I am wondering I have a whistling noise some times, when I turn the fan control for the heater down is when I hear it the odd time,when fan is on high I don't hear the noise

 

[1999 White C5 Coupe]

I am wondering I have a whistling noise some times, when I turn the fan control for the heater down is when I hear it the odd time,when fan is on high I don't hear the noise

You failed to include the make, model and engine of your vehicle - but I’m going to assume it is a an 8th generation Impala.

Follow the instructions in the vehicle owner’s manual to remove and inspect the HVAC cabin air filter (very easy). I suspect you have a clogged HVAC air filter, or there is debris inside the air inlet system.

 

[xtremewhite99]

Sorry the car is a 2013 Chevrolet Impala 3.6 and sometimes it seems to get a bit louder when you turn the steering wheel

 

[1999 White C5 Coupe]

Sorry the car is a 2013 Chevrolet Impala 3.6 and sometimes it seems to get a bit louder when you turn the steering wheel

My error - I though you meant the HVAC was making the whistling sound. You may have a vacuum leak, causing the noise. Is the idle unstable? When you turn the steering wheel, you put a load on the engine - which could cause the noise. Perhaps check all the vacuum hoses? Has there been any work done recently in the engine compartment?

 

[xtremewhite99]

You only hear the slight whistle when blower for heater is turned down low at high speeds you don't hear it, no engine work has been done

 

[1999 White C5 Coupe]

You only hear the slight whistle when blower for heater is turned down low at high speeds you don't hear it, no engine work has been done

I would still remove the HVAC air filter, inspect it and the air inlet area (around the cowl). Ensure the water deflector (under the plastic air inlet grille is in place (after you remove it to check filter) - and that the cowl weatherstrip is firmly in place. Look down into the air inlet area with a flashlight (under the HVAC air filter, after removal) - and see if there are any obstructions or debris that has lodged in the blower fan CAGE.

Good luck.