Hello Jinxie,
It seems you have indeed one 10dB, one 20 dB and two 20dB combined to make 40.
From what you say I'd think the 10dB is the culprit. 60 ok, 70 not?
Remember for the test what someone above suggested: Why not try it with low voltage CC? Very easy to measure the attenuation and to see on a scope if it's noisy!
Not much, just my 2€cents!
Best,
Renaud
