[LAU] Jack issue

my config: Dell Studio Ubuntu 9.04 rt kernel 2.6.29.4-rt15-rt jackd version 0.116.1 tmpdir /dev/shm protocol 24 Ardour 2.7.1 (built from revision 4296) USB iMic audio interface KOrg nanoKontrol cpufreq-set - both cpu's are set to 2.0GHz and userspace I'm trying to get Jack and Ardour set up/optimized for my fall tour I'm using the rt kernel as stated above my Jack settings are 44.1kHz: frames 512: periods 5 latency is not a huge issue for me since I'm only playing back audio for a live mix situation and xruns in Jack seem to be tamed to 0 during playback my Ardour session is 30 minutes in length, has 8 tracks of audio, and the fader levels are assigned to the nanoKontrol everything works fine for the session except at some random point after playing for a while I get a single short burst of AM sideband noise, like I'm multiplying the audio on the mix buss by another audio signal it doesn't happen (so far) more than once per session and it doesn't seem to be correlated to anything like mix buss levels or clipping on a single channel etc is there a setting in Jack that I'm overlooking or has anyone experienced a similar intermittent burst of noise in playback with similar Jack settings? or if this topic has already been discussed can someone point me to a link in the archives? I wasn't able to find anything on a cursory search ================ -- also, I started Ardour from command line when Jack wasn't running and I got three panels in the open dialog box -- one of them being a Audio Setup panel -- is there a way to see this panel after starting Ardour with Jack already running?