I've had this before, a couple of trips on the 7 and one on the 9. 4006 is a perky coach, but the air compressor makes this irritating hum.
UW started today, and the U dist was a zoo. Took 7 minutes just to get to my first stop (45/U Way) from the terminal (12 Ave NE/NE 47 St.) Was 13 down by the time I got to Rainier Beach. At least it was a 9 so I didn't have to go downtown.