Ah ha... well then maybe make a little video or recording of what the noises are sounding like.
and, around when did it start making the noise? the portable is quite the problematic beast.
in the past i have experienced some boards that make some slight noises after a re-cap,
almost like you can hear the CPU processing in the speaker... etc... ever so slightly.
You might want to lightly spray your board down with silicone oil, because 2 years ago i wasn't doing anti corrosion treatments.
Not sure if you are by the salt water, but almost always boards from homes
that are right on the salt water suffer more from currosion then others.