I have Hawk HPS on my Infiniti G37, and I've yet to hear a peep out of them. They're definitely better than the stock pads, and so far there appears to be no downside at all.
A friend of mine has HP+ on his M5 and complains that they make quite a racket every morning.
Mind you the stock pads on my Roadster are often quite noisy for the first couple of stops.