Flashing what colour? Page 26 of manual has info on the NB led's, one is overvoltage the other is temp. Overvoltage has off = normal condition, green = slight, yellow = moderate, and red = high. Temp is off = below 60c, green = 61-80c, red = over 80c.

Doesn't mention that they can be flashing

Interesting to read that for me also, i didn't have a program to give me a NB temp reading, someone recommended Speedfan and said that 'temp 3' was NB, which for me was 61c, but with no light on that can't be my NB temp.