I agree with stu3796 and greathorse. The guineas are noisy, but I've grown to love them and I hardly notice their loudness. I don't care about the hens calling "buckwheat", but I do tend to listen for the alarm call. If you notice a hen calling alarm then you should check around the calling guinea to make sure everything is OK. (Generally speaking, for a slight alarm only the male will call, but if the hen calls alarm also it may be something serious.)
Our neighbors aren't very close either. They're close enough to hear the guineas but the guineas never visit them. (As far as I know, that would be an awful long way to go) We never get any complaints.
And no, guinea cocks do not crow continuously like roosters. The guinea hens almost constantly call "buckwheat" but the guinea cock only calls the alarm.
The first year is always the worst I think. In my experience the guineas seem to be more noisy in their first year than at any other age. For the first year we had the guineas I really started to hate them. They were SO noisy. But that was probably because I was only used to roosters crowing, nothing louder than that. Now in our second year of raising guineas, I love them. It was like once our first guineas reached 1 year old they quieted down a lot.
The only negative things I have to say about guineas is that they may roost in trees at night. (Ours went on a kick of doing this back in February I think? They haven't done it in a while which is good. We've never lost a bird to this but it's still kind of annoying.) And that guineas are so addicting! (But is this really a negative thing? =p)
Overall I love my guineas. They are so fun to watch.