I would say that most guinea pigs are quite silent at night (except the usual noises with the water bottle, and so), but they may be some few females that make very loud noises when they are in heat.
I've got seven females, and there's just one that make those noises when in heat; it sounds like some kind of very loud bird tweeting. The problem is that she does it at night, and I have to wake up two or three times at around 3 or 4 am (and it's quite difficult to wake me up). When I enter the room I see her completely desperate searching for a male, disturbing her mother and two sisters, and being pushed by them, while Abejorro and Vampiro, who are her brother and father and live next to the girls, with the eyes popping out of their heads... It's quite funny now, but not at night!
What I have to do is take and pet her for half a minute, and then she stops tweeting (maybe for all night, or maybe just for an hour...). Fortunately, the heat is just around each 16 days, and she doesn't do that each time. Also, I've just heard about this behaviour in a single web site, which has got an audio file labeled "If somebody knows what does it want, please, tell me", so it seems it is a rare situation.
I'd say the website with the audio file doesn't have all the info about cavies correct, and I think that in this forum you can't post links to that kind of places, is that right?