[NSW] Two questions

["Chris Downs" <cvdowns@ozemail.com.au>]

Two questions for those in the know:

1)    My train to Penrith passed 4 x 81 on 42 hoppers worth of up coalie at
1050 at Werrington yesterday.  A yellow vehicle was positioned between the
1st and 2nd 81s.  Was it likely to have been a dynamometer car or.......?
>From a very brief view it looked like a guard's van.

2)    What is the meaning of the buzzer like noise on DJMs (toward the front
of the cars) for 10 seconds or so during fullish service brake applications?
The train is still usually travelling at around 50-60km/h.  I'm not
referring to the chopper humming but a much louder noise.  [May apply
equally to DKMs and may not apply to all DJMs]

Ta

Chris