I have the following:
Onkyo 805
Supercube I sub
Panamax 5100 pm power conditioner, surge protector combo

Whenever the subwoofer turns on I get this slight pop (thud klunk sound) that comes from the subwoofer. Is this any reason for concern?

that's not unusual; I wouldn't worry about it.

Ross

That's pretty common. I'm guessing, but the poping sound is coming
from stored energy in the compacitors of the power supply.
Nothing to worry about.....vardo