jackd problem (probably)

[Andras Simon]

I'm trying to use rakarrack, which uses jackd, in F7 (yes, I
know, and yes, I will upgrade it real soon now). I first used the
onboard sound (intel-hda) and it worked, except that it gave
terrible noises. On an older (F5) machine with a standalone sound
card, there was no such problem, so I put that soundcard in the
F7 box. (I disabled the onboard audio to make life simpler.) It
does work for non-jackd applications, but rakarrack doesn't even
seem to get any signal, as indicated by the meters.

It's not a mixer problem, because the guitar is clearly audible,
it's just as if rakarrack were switched off (except that it
produces some background noise).

Any idea how to debug this?

Andras