Do I need a noise filter for Senn plug-on transmitter ?

[AAC]

I was shooting a birthday party event video last weekend with Sennheiser wireless plug-on transmitter connected to the DJ mixer and on-camera wireless receiver on my Panasonic DVX-100B.
When I played back recorded tapes after event, I found the audio effect of people using wireless mircophone for announcement/talks was excellent. However, came to the part when the DJ playing music CD as entertainment background music, the sound was deteriorated and not acceptable. The audio input level was way too high. I agreed that I made mistake not to monitor the audio input well when recording. But my friend suggested adding something like noise filter between the wireless plug-on transmitter and DJ mixer next time may help to reduce the noise.... just because the plug-on transmitter didn't have the line/mic input selection.
When I browsed the Senn's web site, I couldn't find such device.
What's that device ? Does it really matter ?
I would like to learn from your expertise to rectify such problem in future. Many thanks.

[jagabo]

Your talking about an audio attenuator, not a noise reducer:

http://www.minidisco.com/10dB-PAD

Obviously, that particular device is meant for a 1/8 inch stereo pin-plug. You'll have to get what's appropriate for your setup.