I know this is about 3 years late, but I just had the same issue with my RC-64 II, and I spent days trying to figure it out, and a month of not being able to fully enjoy my speaker. I finally became extremely frustrated and I just barely found the solution. The extents I went to trying to figure this out were very exhausting, one of which led my here to find this forum post where I was sadly let down to see there was no answer. Now that I've figured it out, I thought I would post my findings to save future RC - 64 owners a lot of time. What it was, was resonance coming from underneath the speaker from two little small holes that I'm guessing are there from being factory made. Knowing that the reference I RC 64 and the reference II RC-64 are very much alike, I'm assuming that there are two holes on the bottom of the RC-64 reference I series as well. If you are using the rubber feats that klipsch sends with all their speakers, then that is most likely your problem and you need to simply remove them. I know it sounds so simple... but if you never had this problem, then you have no idea how hard it is to pinpoint where the squeak is coming from. During low frequencies, the squeak actually resonates from both inside and underneath the speaker which makes it confusing and difficult to find. My RC-64 II is brand new, and I thought I had bought one that was defective and was about to send it back which I was dreading. I was thinking all the possibilities. I thought it might not be getting enough power, I thought I had blown the tweeter, I thought I had set the frequency too low, I even took one of the subs off to see inside thinking that it was maybe the driver rubbing against the poly-foam and even cut some out! Frustrated, I reattached the speaker and started adding rags under the speaker hoping to maybe tame the problem, and it started to dissipate. That's when I realized what the problem was. Once I took the feat off and put the speaker on top of a blanket the squeak was gone completely. I hope this helps someone someday.
