It's a bit uncommon to be hearing sounds like that if you're just starting and not meditating for very long - especially if you weren't looking for them. But yes, those sounds happen to others, including me. Yoga teachers state it is a sign of the nadis (energy channels in the body) being purified.

There's a practice called "nada yoga". It actually uses these sounds as a way to go deeper into meditation, because as you've found they feel quite good and absorb your mind into them. Some scriptures consider it the fastest method of reaching "samadhi".

Some texts give descriptions of the actual sounds that will be heard, for example the Hamsa Upanishad lists ten sounds:

1. Chini nada - sounds like the word "chini"
2. Chini-chini nada - sounds like "chini-chini"
3. Ghanta nada - sound of bells ringing
4. Shankha nada - sound of a conch being blown
5. Tantri nada - sound of a lute
6. Tala nada - sound of cymbals
7. Bensuri nada - sound of a flute
8. Bheri nada - echoing sound of a drum
9. Mridanga nada - sound of a double drum
10. Megna nada - the roar of thunder

Though it is really just an indication, since these are subtle psychic sounds, and we can perceive them slightly differently as individuals. Just for an example, one of the earlier sounds I heard was what I would describe as a sound similar to the sound of a dial-up connection. I have never heard that described anywhere else (and of course such a sound didn't exist when these teachings were first written)...but that is what I personally experienced.

Just for more informational purposes, if you decide you want to go this route (which I would suggest might be worth your time, since you came upon these sounds so readily).

The practice of nada yoga is prepared for by performing bhramari pranayama to draw the mind inwards (this is optional, though). That link doesn't mention specifically, but the important point practically is to keep your teeth apart as you make the sound, this allows it to reverberate in the head. The main point is to have the sound reverberate in the head and to focus on it. It doesn't matter how loud it is. You can also make a particular sound while you inhale.

After a few minutes of that, you stop. But leaving your hands positioned as they are, you just begin to sit silently and listen for the inner sounds. Typically (in scripture and in my experience) they will be primarily heard in the right ear. When you hear a sound, particularly one that pleases you, you focus your mind on it and become absorbed into it. After practice and with time (can take weeks or more of daily practice) you will begin to hear another sound, more subtle and quiet compared to the louder sound you had been focusing on. When that happens you shift your focus onto that new quieter sound, and gradually it will become louder...and later another quieter sound will be heard. And so on. In that way you keep hearing subtler sounds and absorbing your mind inwards more and more.

A slightly more "advanced" way is to in addition to the above, you inhale and hold your breath while doing it. That's taking advantage of something we naturally do, if you ever thought you'd heard something you might notice yourself holding your breath as you listen for it. Holding the breath also purifies the nadis, which as I said earlier is what the yogis consider the sounds initially heard (the gross, "louder" sounds) to represent. I wouldn't recommend doing that at first if you haven't done breathing exercises of some kind before, since it could just end up a distraction and you don't want to strain yourself.

Most people when starting out don't tend to hear the sounds on the first try (I say that for others later who might read this). You do not need to maintain the hand positioning or even use it either after bhramari, as it can be difficult for people to hold their arms up for too long like that. But it is advised to do as long as possible, because it further aids the mind in going inwards into the sounds.