Mystery Noise Honda Accord

My girlfriend has a 2001 Space Odyssey Honda Accord. We were working in her garage and we both kept hearing a weird noise. It was darn near impossible to find the source, as it did sound like it was coming from the car but listening directly to the car would fool you.

The noise sounded like cell phone vibrating on a table. It consistent about every 2 mins. I finally found the noise by putting my ear directly on driver side rear qtr. panel. I then looked under the car and found a electrical motor and a box for the source of the noise.

There was a small round cylinder disconnected from a hose and a bent mount. I reconnected the gizmo to the hose, whacked the bracket (aligned it) and put the gizmo back on the device. All the hoses seem to be around 1" I.D. This was at the rear of the car next to break lines.

OK What is it?

My guess some kind of vacuum accumulator or some kind of pressure chamber. I have no freaken idea what this could be. So I am throwing out to the all wise and helpful forum.