Transmission "clicks" on downshifting into first?

[readallthebooks]

1999 base V70. Driving around with the windows down I noticed that when the transmission downshifts into first, around 12 MPH, a single audible "click" can be heard from the engine bay. It's not loud enough to be heard with the windows up. It almost sounds like a relay closing? and it's very definitely only a single click. it also doesn't happen if i put the car in winter mode so it seems to be related to first gear? the transmission otherwise performs great, no shuddering, no slipping/flaring no clunking or anything at all.