This is actually a known issue and is covered by a TSB. My car has this problem also and basically makes this noise any time I am braking at low speeds. It is something related to a brake pump or valve that is located within the dash immediately to the left and below the steering column.
Someone else posted the TSB info about 3-6 months ago, I think, but I couldn't find the post.
2007 Camry V6 SE
, Blue Ribbon Metallic, UR Strut/Sway Bar, K&N SRI, Magnaflow mufflers, H&R Springs, TSW Nurburgring 18x8, Reus Sound System, More