[LAU] Crackles in audio - how to troubleshoot ?

Hello, Suddenly the audio started crackling. I was listening to a youtube tutorial (firefox) and it started. Bitwig and Renoise were running but not playing anything. I looked at the log files (syslog, kern) nothing relevant. Card is 10101LT. jackd runs at about 10.3ms latency (last time I checked using jack_iodelay), so it run as: /usr/bin/jackd --sync -T -P95 -ndefault -dalsa -dhw:M1010LT -r44100 -p128 -n2 scaling_gouvernor all set to performance. Interrupt prio looks OK: PID CLS RTPRIO NI PRI %CPU STAT COMMAND 436 FF 90 - 130 1.6 S irq/18-snd_ice1 47 FF 50 - 90 0.0 S irq/9-acpi limits audio.conf is: @audio - rtprio 95 @audio - memlock unlimited Interrupts servicing for all 4 CPUs (i5) : 0: IR-IO-APIC-edge i8042 4: IR-IO-APIC-edge 8: IR-IO-APIC-edge rtc0 9: IR-IO-APIC-fasteoi acpi 12: IR-IO-APIC-edge i8042 18: IR-IO-APIC-fasteoi snd_ice1712 jackd and pulse processes: /usr/bin/pulseaudio --start --log-target=syslog [pulseaudio] <defunct> /usr/bin/jackd -T -ndefault --sync -T -P95 -ndefault -dalsa -dhw:M1010LT -r44100 -p128 -n2 The pa zombie was there way before the crackling started. Not sure if this is related. The pulseaudio jackd sink is active and can be seen in qjackctl. So it seems OK. But the audio is full of crackles. In firefox, as well as Bitwig and Renoise when now something is played. Of course, when the machine was started some audio was played in both Bitwig and Renoise and it was fine. Then I watched a youtube tutorial and bam, after maybe 15 minutes, all audio output is full of crackling. Since the log files shows nothing. How is troubleshooting information gathered ? There should be some SW system component that can be probed, somwthing that could be observed. - or is it that the 1010LT is going awry ? Can this happen at all ? Thanks for suggestions and comments ! Cheers.