The board that was installed is the ps3 steam upgrade kit that anyone can purchase from MTH, item 50-1911. It was installed in the tender.
The sound file used was for fef nothern item 20-3044-1 upgrade file.
The 3 chuffs are evenly spaced. One thing I noticed is that the main chuff or the first one in the sequance that sounds a little more deeper than the rest moves 1/4 turn earlier for every sequence. It never plays the 4th smaller chuff and starts the main chuff 1/4 turn earlier. This is with a chuff rate set to 4.
Changing the chuff rate to 5 or higher only makes the sequence go faster, more chuffs per revolution of wheel. The pattern is still the same chuff 23 chuff 23.
I have attached a video with sound so you can see and hear better as to what is going on.