I bought an iFP-799 for recording with an external mic, and I heard that same cyclical noise in my recordings. It was more noticeable on some recordings than others even though the settings were the same. I downloaded every firmware version available, but the noise was there when recording on all of them, even without a mic attached (so it's not the mics fault). Changing the bitrate changed the speed of the noise somewhat, but it didn't go away.
I thought perhaps I had a faulty player, so I returned it for an iFP-895, but have had the same problem. I think the problem is in the internal mic preamp. Other than that artifact, the recording quality is good, but I was surprised I hadn't seen it mentioned in these forums or other internet posts touting the recording features of the iFP 7** & 8** series.
Also Jthor - I'm not sure what you mean by recording in the field, but if you want to improve your recording quality, an external mic will sound better than the internal one, but that noise artifact will likely still be present.
Here is a great recording guide for the H** series hard drive players, but most of what is discussed applies to the iFP line as well
http://www.misticriver.net/showthread.php?t=5072
Different external mics are discussed here. I'd advise staying away from the sony line because they are not very sensitive. I have the ECM907 from sony and usually have to record on full gain, which means the recording glitches are louder. I think the Sound Professionals seem like a good place to find an external mic:
http://www.soundprofessionals.com/cg...cgi?category=0