Hmmm. Let's take a look to the well known picture from Polmar.
According to it Alfa should be roughly equvalent to Permit class in basic noise level (but Alfa is still more noisy when running at 40 knots of course). Also even early Akula is slightly less noisy than the Sturgeon class, which is still in service in 1984.
Also I've seen the exact meaning of the Charlie class noise level in the Russian sources. There it's claimed to be equal to 110 Db in the audible part of the sound spectre (at top speed). But this information seems to be doubtful to me.
