Hi - this looks interesting! Its a shame you couldn't post a portion of the I/V to hear what we're sealing with here - if it is a contant frequency noise, it would be easy, but if it is spectrally shifting, that's more of a problem.
I used to be a freelance reporter for BBC Radio so have had problems like this to deal with, and am happy to try and help you out.
I'm in London, 55 yrs old (so loads of experience) and happy to try this if you can send me a sample - or all of it.
Kind regards
Bob