Rythmic, washing sound on idle

[jetboy]

Just took the car out of the garage and let it idle a bit while checking something.. and I hear this rythmic, washing sound from probably the left side. Like a pump pushing some fluid, totally in rythm, interval maybe 2-3 seconds. From inside the cupè.

It first sounded like my head was playing at very low volume, like when you can vaguely hear the snare drum.

Car was cold. Out of time so I couldn't pop the hood but will do this soon. Any ideas? I think maybe the window wash fluid reservoir?