I like Tangoya-san's answer. I'd just like to add that ぬ can be considered an archaic or poetic form of ない. I was just wondering, did Tangoya-san mean that the ん form sounded more FORMAL or INFORMAL than the ない form? Because I think even though people in Western Japan would say わからん, they would still write わからない unless they are writing a dialogue.

'隠せぬ' means 'unable to hide'. 'ぬ' is an auxiliary verb that has the same meaning as 'ない'. It can be used either before a noun or noun phrase as in that lyrics, or at the end of a sentence to end it. When used at the end of a sentence, people usually pronounce it as 'ん'. わからぬ = わからん = わからない = do not understand 読まぬ = 読まん = 読まない = do not read The ん form sounds a bit more formal than the ない form, and is more often used by old people or in Western Japan.

Thank you Marie-san, and sorry Certainly but what I wrote below contains an error. The ん form is a colloquialism so it is naturally LESS formal than the ない form.