Whumpfing in Tahoe Donner XC area

Heard occassional whumpf and cracking near ski tracks on E facing 18 degree slope at 7150'. This is near treeline but in a large open area. I could feel a crust layer about 30 cm down. I did not dig to investigate, but based on watching yesterday's weather I would guess a rain crust. New snow was starting to slightly slab up but still mostly unconsolidated. 

After climbing ~200 ft, the crust was much less distinct and I observed much less cracking/whumpfing, even in areas where the new snow had become wind-effected.