Sorry to hear that, but "sizzling" is actual "ringing", asociated with Kevlar tweeters. Look to upgrade to III, with new driver and ScanSpeak tweeter. You will love it.
"Sizzling" tweeters at high volume?
I have my new SFC-1 tube amp (Svetlana El34) 50wpc. my speakers are ACI Sapphire II (Focal TK-120 kevlar tweeters)rated 15-150wpc, 90db with imp. of 6ohm. On some recordings (Live at the Greek, Tim Haggans...)snare drums, and trumpet would start to "crackle", at volume level past 12 o'clock. On other CD's it doesn't(Kind of Blue)