My Galaxy was doing this same annoying random 2-tone beeping thing. I found the problem, at least on my tablet.
When I bought the tablet, the sales person set up an obscure email account which was never used by me. Four spam addresses were sending me 200+ emails per day. Once the email limit was reached the tablet would beep for every additional spam.
I added the addresses to my spam filter, deleted all the emails and the problem went away.
Dave