実は、大きな声で言えませんが、ここ最近このビーチで若い女性が盗撮されたうわさがあるんです。

、、。

Actually — I can't say this too loudly, but there's been a rumor lately that young women are getting secretly photographed at this beach.

Literal

Actually, big voice [with-で] cannot-say[but-が], recent this beach [at-で] young woman [subject-が] secretly-photographed rumor [subject-が] exist-[explanatory-んです].

Concerned confidential tone. 実は 'actually, to tell the truth' opens a confidential disclosure. 大きな声で言えませんが 'can't say this in a loud voice' is a set idiomatic preface for a secret or sensitive disclosure — not literally about volume. 盗撮 is a compound 盗 'steal' + 撮 'photograph,' meaning 'secret/illicit photography' (including the crime). The long relative clause [若い女性が盗撮された] modifies うわさ 'rumor.'