I bought a Price Pfister with pull out sprayer a few years back when I replaced our counter tops and tiled the backsplash. It was whistling the second I started to use it. I put up with it for a few days before I had enough and took things apart to see what was going on. In the hose end, I believe its on the sprayer end but it might of been where it connects to the faucet body, was a little white restrictor (I still have it somewhere) to reduce the flow, conserve water, ect. Popped right out with a pair of needle nose pliers. Whistling stopped. Put it back in, whistling came back. So I took it out because I just couldn't stand the whistling. Pressure out of the faucet was fine so it worked for me.
Here's a pic. That's the Price Pfister I have.
Disclaimer: I'm not advising you to create a higher flow, anti"green", pressure washer here. It's totally your choice to modify your faucet in any way. Just relaying my experience. Had I of still had the box I would of probably just taken it back. I just couldn't stand the maddening high pitched whistle.