My daughter just turned 6mos. and is doing the EXACT SAME thing.
She will make noise, then get louder and turn it into a high pitched screetch. She loves attention too!
It's normal they just found their voices and are experimenting with it. It's a phase. Last week mine was into making kissy noises with her lips non stop, the week before she was into sticking her tongue out.
I do tell my 6mo.old to shhhh... no screaming! I'm sure she doesn't understand but because it's so annoying and will not be tolerated as good behavior when she's a toddler I've decided to already show her mommy doesn't think it's cute. My older daughter was saying shhhhh this is a library ssshhhh it is very annoying. I don't give her attention for her screams, her kissy noises and being cute yes lots of attention.
If you don't like the screaming then just say ssshh. make lots of unhappy facial expressions to show her that mommy doesn't like this. Don't give her attention for this or she'll go nuts with it. Then when she does something cute or funny give lots of attention. That's my theory anyways. I'm sure alot of people will disagree that you shouldn't be so harsh on a baby but I believe in starting young. Nip it now before you have a toddler that thinks it's cute.