Is this thump normal?

[pyonc]

With a dummy load, (aka 8 ohm resistor) attached to the output, you also attach the leads of the Fluke to the output. Depending on polarity of the DC offset voltage, you may need to reverse the leads on the Fluke.
Baron030

Thanks a lot for your kind explanation.
As I'm not that familiar on this tech thing, can you identify the output with something like an arrow on the circuit board?

By the way, in the manual on D.C. at output section, I see:

1. +_ 0.1 volt normal
2. + _3 volts adjust R9 for 0 volt D.C.

So, I guess you're right. R9 is the DC offset voltage adjuster.
Attached is a brighter pic of SE408S where once can see the R9 more clearly. I see sort of bolt-like cross in the center, which I think is intended for adjustment, right?