I just bought a Hartke 210C combo. The problem I am having is that anything played under about 110 Hz makes the speakers flutter terribly. I wasn't sure if this was the way it's supposed to sound or if I had a problem. I connected a signal generator to the input add swept the freq from 20-200 Hz while monitoring the output signal to the speakers with a scope, looking for distortion. The input voltage was 76mVrms (215Vpp). At 1 on the gain things were pretty good however the output signal drops off dramatically below 80 Hz. When I got to 3 on the gain anything below 80 Hz just made the cones flutter. I could hear the fundamental faintly but most of the sound I heard was flutter. The output signal looked like a perfect sine wave so I assume the speakers or cabinet design is the issue. I spoke with someone from the factory and he said it was normal for it do it at little (which surprised me), but he said that sounded excessive. Later I got another call and that person said it may be the dust covers coming loose. I went and checked - all looked good - sealed all around. He said I could return it to the factory for warranty work. My dilemma now is that this is a ported cabinet which I've never used on bass and am wondering if this is just the way it's going to sound and they'll find nothing wrong. I have a sealed enclosure GK combo and also other sealed cabinets and I don't have any problems. I did a lot of checking before trying a Hartke. Surely there must be something wrong. I don't believe they would sell an amp with an EQ pot centered at 80 Hz, designed for bass, and a gain that goes to 10 if it can't reproduce the bass instrument fundamentals (E thru G, 42-98 Hz) with out it sounding like a flock of birds taking off when pushed above a gain of 3. Does anyone else own one that could tell me if they all sound like this or have I made a terrible mistake? I'm not trying to push the fundamental but I do like it to be there without it sounding like I'm playing through a fuzz box. I would appreciate any opinions or experiences others have had. I don't know what to do or what to expect from a factory warranty look over - it costs a lot to ship 63 lbs.