Fluellen

Hello, I am wondering if you could help me troubleshoot my issue. I’ve read lots of posts about humming problems with subs, but my issue appears to be a tad bit different. I just bought a R-12SWi. When I plug the unit into the power outlet, I can hear a low hum coming from the sub. The hum gets louder when I turn up the gain control on the sub. It also gets louder if I touch the Phase and/or On-off flip switches on the sub with my fingers. All the while the sub is not connected to the receiver, so there should be no signal to the sub whatsoever. I’ve tried different power outlets in the home, with no change. The sub otherwise works fine. Note, the hum is very low and only audible if I put my ear within 2 feet or so of the sub. It is not audible at all when music is playing. But am still concerned that something isn’t right. Is the sub’s amp defective? Thank you in advance for any insight you can provide!