MRI background noise filtering

[Fallout1]

Hi All,
I've read the Audacity Wiki tutorials for Noise Removal and Notch Filtering and am still having some trouble with getting my file to sound decent.
I'm dealing with voice recordings taken with a microphone inside an MRI machine and am facing high pitched constant sound as well as extremely loud pulsing (kind of like a jackhammer) background noise with intermittent voice responses. I've done the standard noise removal techniques and notch filtering but I think since the sound itself rises and falls in pitch (albeit quickly) , Audacity may have some trouble (as opposed to a constant static for example). Can anyone think of how to go about this? I've attached a small portion for testing as well as a picture of the waveform. (Background noise from the left and needed voice response @ 17 sec)

Thanks for your help in advance.

[Fallout1]

additional info: When running a plot spectrum analysis I get a rough plot, rather than the smooth example given in the wiki. Any way of dealing with a rough spectrum or does one just isolate a large range of peaks?

[steve]

The whistle can be reduced quite a bit with notch filtering at 3720, 2360 and 1588 Hz.
The "jackhammer" noise is a non-starter. As far as "Noise Removal" is concerned, that is not "noise", it's a performer in your show.
You may be able to get some degree of success at removing it using ExtraBoy (from elevayta.net - commercial plug-in / free demo version available) but don't expect too much.

[Fallout1]

Alright, I'll give it a try.

Thanks for your reply