Servus Lisa,
das war ein "bekanntes Problem" bei den U-Analgen. Die Datenleitung lag auf dem board zu nahe an den Audio-Leitungen. Deswegen gab es das Knacken.
Es gibt mehrere Möglichkeiten: Hier mal das "offizielle bulletin":
Help File Category: Network Monitoring Signals
Network Monitoring Signals
The UA888 (or UA111) uses two low-level signals to continually monitor and control U4 receivers. The first signal is used approximately once per second to poll the receivers for battery status information. The second signal is used to poll the receivers for all other functions: RF and audio levels, frequency, squelch, name, etc. The second signal occurs many times per second to ensure very accurate monitoring and metering information.
In quiet listening environments, these two low level network monitoring signals may be audible. This signal can be lowered by as much as 10 dB relative to the desired audio signal by using the following gain structure procedure:
1. Turn the output level knobs on each U4 receiver fully clockwise.
2. Select either mic level or line level output on the back of the U4 receiver.
3. Adjust the input trim on the next device in your audio chain appropriately to avoid clipping.
4. If the U4’s output overloads the input of the next device, add an attenuator between the devices. The transmitter gain can also be adjusted, if necessary.
The above procedure retains all features of the UA888 Network Interface System because the network monitoring signals are perceptually reduced, but not entirely muted. If desired, however, the network monitoring signals can be muted by the following two software options:
Muting the Network Monitoring Signals using UA888 Software
Option A: Mute the battery status monitoring signal only.
In this option, RF and audio metering continue to function as before, and group/channel, frequency, and squelch continue to be displayed. The battery status bars will be “grayed out”. Receivers on the network can still receive commands from the UA888. Activating this option will eliminate the more predominant component of the UA888’s network monitoring signal.
Option B: Mute all network monitoring signals
In this option, the RF and audio level metering will be “grayed out”, along with the battery status bars. Only the group/channel, frequency, and squelch settings continue to be displayed. Receivers on the network cannot receive commands from the UA888 using this option. Activating this option will eliminate the less predominant component of the UA888’s network monitoring signal.
Service Department Solutions
If the perceived monitoring signal still cannot be adequately lowered for your particular application, please contact the Shure service department to discuss additional options. Circuit board modifications to U4 receivers are now available for further reductions in the network monitoring signal level.
Ob sich dieModifikation noch lohnt ist natürlich fraglich. Du kannst aber gerne unseren Service diesbezüglich kontaktieren.
http://www.shure.de/supportdownload/reparatur_ersatzteile
Besten Gruß
