Sennheiser ew100 picked up noise from interview background

[AAC]

Last weekend, I taped two video footage by Canon XA20, one was interview in the boardroom and the other was academic presentation in classroom, with sennheiser ew100 clip-on lavalier to pick up voice . I didn't hear anything wrong from the headphone during video recording. The audio was good when playing back on computer. However, I could hear low noise behind the speech or talk. The noise is like low frequency "wuuuu, wuuuu" through out the whole footage. At first, I guessed it was caused by air duct central air conditioning but later I found out there was no such thing in the room.
Did I do something wrong ? or the input level on camera was too high ?
How can I remove noise from the footage ? I use PE12 to edit video.
Many thanks.

[AAC]

When testing in other room, the noise is gone. It could be interfered with loud speaker in the lecture room.
How can I get rid of this noise ? I only have Adobe Premiere Elements 12.
Thanks.

[redwudz]

You would likely have to extract the audio out and use an audio editor like the freeware Audacity or similar and the filters it has. Then mix it back in with the video.

[smrpix]

Please post a short sample so we're all on the same page.