Lewm, I have not experienced cover machine screws, for example, loosening after being tightened, but have often found screws and feet loose and sometimes missing on new gear which is the basis for properly tightening everything. Properly tightening the items decreases resonance issues, such as that resulting from a loose cover. I did find that my drivers loosened up after a period of time, which required tightening as well, even on a subwoofer replacement driver I personally installed and tightened. A metal to metal interface is generally a transmission conduit which the PTFE tape helps defeat similar to vibration isolation products. It also eliminated the play in my Raven motors feet which was quite extensive. However, sometimes a metal to metal interface may be beneficial in a system as well. I also found much to my surprise, that Cardas caps which I have been routinely using for years, was actually detrimental in my system. I would certainly like to be able to utilize some type of cap over the jacks, and will probably try plastic or rubber ones at some point, but it's unfortunate that the caps will no longer be going back on my active equipment, as I have accumulated quite a few of them. I have no rational explanation as to why installation of the caps was detrimental, as it is simply a cover. However, I live in the Washington DC area and I may have been picking up some type of signal or interference through the caps, but other than that idea, I am clueless. The ears are the final judge and jury.