Also many SS amp manufacturers use something called a Zobel Network. It amounts to a series inductor (coil) and a capacitor or just the inductor. This is used as a filter and is located just after the output devices prior to the signal hitting your speaker terminals. It could be as simple is one of your pieces of audio gear is unstable for some reason. I once found a fet constant current source was acting like an R.F. generator in an old CAT preamp. Once a device becomes non-linear it's possible it can oscillate.
Ultrasonic Oscillation
Hi. I have had recent issues with my Snell Ds, tweeters not working. Anyway this led me to test of all of my equipment including my GMA Europas. Their tweets were dead also. I dropped an email to Roy at GMA and he suggested that I may consider the possibility of ultrasonic oscillation in either my amp or pre-amp. They are the Odyssey Candela pre amp, and Stratos amp. Could you please explain what it is, and more importantly what are the causes. Soon I'll get a diagnostic locally and sending the pieces to Klaus for repairs if needed. I look forward to your insights. Thanks much, Dave