WTF is this rattle?!

[five-alive]

I've had some new rattles pop up in my '03 SR5, but one is really annoying. Its coming from under the dash near the bottom of the windshield and it sounds just like rain drops are hitting the windshield. The first time I heard it I thought what the hell there isn't a cloud in the sky?

Any thoughts? I had ants a few weeks ago and I think they are eating my foam/glue causing these rattles.

 

[wombie]

If the noise is coming from the driver's side then I have a suggestion: Put your truck in park, open the hood, and get a buddy to press the brake pedal. You might be hearing the brake booster/master cylinder whirring. They can get pretty noisy. Only fix (as far as I can tell) is replacing the master cylinder. At least that's the only thing that worked in my truck.