The way you are discribing them, they definitely do sound like Pionus, but like others said, I have never heard of any wild pi's in North America. I do know that in Fla ya'll have wild quakers, and they can certainly sound like some sort of a monkey! Here is my Simon when we first got him....did they sound like this?
YouTube - Full metal beak Only thing is that quakers have very long tails, so that part doesn't fit. I did read ya'll also have wild cherry headed and nanday conures, but again, they have long tails. I hope you can get a pic or vid of them!