[joeysteele]

I am not 100% sure what I would do but if you heard nothing and no one else did then it seems odd.
If you cannot get an answer at the door then that's of concern too,if they are usually there.

You are only being neighbourly after all and I guess if I felt something was as odd as you describe and that there seems no explanation for things as they are then there is no harm in having someone check it out.
I guess,although some people take exception to others poking their nose in,if you know things are not usually like this then I would personally rather be safe than sorry and have it checked out just as a precaution.

If I kneEw the people even more so would I do that. However, if you know or think they are or can be hostile people who live there then maybe my way is not an answer in this case.