That is kinda strange, usually a bad regulator will make noise when using gas, and will make that noise if it's leaking gas, but you said you can't smell any gas. The regulator should be replaced, you don't want a gas leak. The other thing you can do to definatly verify that is the noise, is to pull the oven out from the wall and shut of the gas valve at the wall, if the noise persists, then it is something else.
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