How would I know if I used jack? Not many jack-packages installed though:
dpkg -l | grep jack
ii libjack-jackd2-0:i386 1.9.9.5+20130622git7de15e7a-1 i386 JACK Audio Connection Kit (libraries)
What other packages might be relevant? There are a lot:
aptitude search jack
p alsaplayer-jack - PCM-Player für ALSA (JACK-Ausgabe-Modul)
p azr3-jack - drawbar organ simulator
p dssi-host-jack - Example of DSSI host
p fxcyberjack - Graphical diagnostics and maintenance tool for Reiner SCT Cyberjacks
p gjacktransport - access to the JACK's transport mechanism as touchable slider
p jack - Liest und encodiert CDs mit einem Kommando
p jack-capture - program for recording soundfiles with jack
v jack-daemon -
p jack-keyboard - Virtual MIDI keyboard for JACK MIDI
p jack-midi-clock - JACK client that sends MIDI beat clock pulses
p jack-mixer - JACK Audio Mixer
p jack-rack - LADSPA Effekte »Rack« für JACK
p jack-stdio - program to pipe audio-data from and to JACK
p jack-tools - Diverse Werkzeuge für JACK: dl, record, scope, osc, plumbing, udp, play, transport
p jackd - JACK-Audio-Verbindungs-Kit (Standard-Serverpaket)
v jackd-firewire -
p jackd1 - JACK Audio Connection Kit (Server und Beispiel-Clients)
p jackd1-firewire - JACK Audio Connection Kit (FFADO backend)
p jackd2 - JACK Audio Connection Kit (Server und Beispiel-Clients)
p jackd2-firewire - JACK Audio Connection Kit (die Backends FFADO und FreeBoB)
p jackeq - routes and manipulates audio from/to multiple sources
p jackmeter - a basic command line meter for the JACK audio system
p jacksum - computes checksums, CRCs and message digests
p jacktrip - A System for High-Quality Audio Network Performance
p libbio2jack0 - oss/alsa to jack porting lib - runtime files
p libbio2jack0-dev - oss/alsa to jack porting lib - development files
p libbjack-ocaml - OCaml blocking interface to jack audio connection kit
p libbjack-ocaml-dev - OCaml blocking interface to jack audio connection kit
v libbjack-ocaml-dev-pzcy5 -
v libbjack-ocaml-pzcy5 -
p libifd-cyberjack6 - REINER SCT cyberJack USB chipcard reader user space driver
v libjack-0.116 -
p libjack-dev - JACK Audio Connection Kit (Entwicklungsdateien)
v libjack-dev-session -
i libjack-jackd2-0 - JACK: Bausatz für Audio-Verbindungen (Bibliotheken)
p libjack-jackd2-dev - JACK Audio Connection Kit (Entwicklungsdateien)
p libjack0 - JACK: Bausatz für Audio-Verbindungen (Bibliotheken)
v libjack0.100.0-dev -
p libjackrabbit-java - content repository implementation (JCR API)
p libjackson-json-java - streaming fast powerful standard conformant json processor in java
p libjackson-json-java-doc - standard conformant json processor in java - API documentation
p libjackson2-annotations-java - fast and powerful JSON library for Java -- annotations
p libjackson2-annotations-java-doc - Documentation for Jackson-annotations
p libjackson2-core-java - fast and powerful JSON library for Java -- core library
p libjackson2-core-java-doc - Documentation for Jackson-core
p libjackson2-databind-java - fast and powerful JSON library for Java -- data binding
p libjackson2-databind-java-doc - Documentation for jackson-databind
p libjackson2-dataformat-smile - fast and powerful JSON library for Java -- Smile dataformat
p libjackson2-dataformat-smile-doc - Documentation for Jackson-dataformat-smile
p libjackson2-dataformat-yaml - fast and powerful JSON library for Java -- YAML dataformat
p libjackson2-dataformat-yaml-doc - Documentation for jackson-dataformat-yaml
p liquidsoap-plugin-jack - audio streaming language -- JACK plugin
p multimedia-jack - JACK (Jack Audio Connection Kit) and ALSA related packages
p projectm-jack - projectM JackAudio module
p pulseaudio-module-jack - jackd-Module für den Audioserver PulseAudio
p pulseaudio-module-jack-dbg - jackd modules for PulseAudio sound server (debugging symbols)
p qjackctl - Benutzerschnittstelle zur Kontrolle des JACK-Soundservers
p qjackrcd - Qt4 application to record JACK server outputs
p silentjack - silence detector for the JACK audio system
p slv2-jack - Jack support for LV2 plugins
p snd-gtk-jack - Sound file editor (GTK+ user interface - JACK)
p tuxguitar-jack - tuxguitar plugin for sound playback using JACKD
p vlc-plugin-jack - JACK-Audioausgabe-Erweiterungen für VLC
p xmms2-plugin-jack - XMMS2 - JACK-Ausgabe
And furthermore: why would xnoise be installed in the first place, when it doesn't work?