I have a Tascam DR60DMkII recorder and preamp into which I've plugged a Rode NTG2 shotgun mic. I've been experiencing a slight hum or noise when I turn up the gain to gain to where I get a nice clear audio signal. I can dial down the gain and get ok voice quality but I like the crispness of the audio at the higher gain. I also find I can eliminate or reduce the noise in an audio editor quite a bit but who wants to mess with an unnecessary step in audio production?
This web article is a decent more comprehensive discussion of audio problems. In general, beware of nearby cell phones, monitors, fluorescent lights, speakers and other such sources of radio frequency interference (RFI).
Sound and audio connectors are not for the faint of heart I've found but, as one YouTuber observed, so so video can still work if you have good sound but not the other way around.
A+ for the Tascam, btw. The menus and controls can be a bit daunting if you're new to audio but once you practice a bit they're not a problem. It eats up batteries so you definitely want to use rechargeable batteries. I bought a LifeCharge external 16,800 mAh battery and that eliminated the batterys' running down during any one day of shooting. Tascam tech support is excellent, let it be said. Very decent folks.