pronunciation of 人 - regional or gender differences? To my English tuned ear, these audio files of people pronouncing 人 sound very different.

My colleague (a native Mandarin speaker) insists they are the same sound, and thinks I am just confused because one speaker has a higher pitched voice. He said something about one speaker having a more feminine voice, but I'm not sure which of the two he meant.

I'm happy to accept that I'm tuning into a non-key part of the phoneme, but to my ear these sounds sound consistently very different from speaker to speaker.

The Wikipedia page on Mandarin phonology has an explanation for the variation:

ɻ (a retroflex approximant) varies as ʐ (a voiced retroflex fricative), depending on the speaker.

I've also heard other speakers where a sound more like the English Y was more prominent. Is this difference something native speakers notice? Is it considered a regional variation, or as my colleague seems to be suggesting that one is more masculine and the other more feminine?
The two speakers sounded like they were both saying 人 with a [ ɻ ]. One's voice was higher pitched and the recording conditions were different though. In practice, you're going to run into pronunciations way more divergent than those. All the people I've met from 青田 say it with a [z] (note: not a pinyin "z"). Also, I've run into a few people who use an [l]!

My advice: Listen to a lot of people, chat with a lot of people. You'll pick up on which distinctions are important, which aren't, and which are regional.