Intermittent whooshing sound from motor. Losing coolant as well

What is your question?

I have a 2000 GMC Sierra 1500. I have a sound that I can't pinpoint because it's intermittent. I have asked around and some think it's the intake manifold leaking. The sound is similar to a relief valve blowing off excess pressure then reseating. I have coolant leaking but don't see any leaks in the system. Any ideas would help.