I heard a thunder. / I heard the thuder.

[englishhobby]

Is there any difference in the use of articles in the following context:

We were going back home after a day's walking tour to the forest. The sky was getting darker. A strong wind began to blow and we heard a / the thunder.

I know that "thunder" is uncountable and it's better to use "a clap of thunder" or a "roll of thunder", but still, can one just use "thunder" alone and sound natural?

[5jj]

You can hear thunder but not a thunder.

[englishhobby]

And can I hear the thunder?

[5jj]

And can I hear the thunder?

Yes. It's unlikely in your sentence. Not only has there been no previous mention of thunder, but no real mention of a storm.