When I brake I get a whistling sound, what could it be? on 2008 Nissan Altima

Whenever I brake, no matter the speed I get a loud whistling sound.. What could the cause of this be?

Asked by for the 2008 Nissan Altima
This is probably from the brake booster. It is located in the engine compartment, but the noise will be heard near the brake pedal.
Screeching is different. This could mean the brake pads are in need of replacement, if it is more of a grinding noise, then you may need brake pads and rotors. I would get the brakes inspected to know for sure! Good Luck!
Ok.. I could be confusing whistling with screeching... would that be the same thing?
Thanks man, I appreciate it.