5mnth ds's knee has been clicking all day something or nothing to be concerned about?

[slinkee]

He doesnt seem bothered by it but it has been clicking all day and Im a bit worried. A friends 18 mnth old sat on his legs 2 days ago so I was worried that may have done something as he cried at the time. Thanks in advance.

The fact that another child sat on his legs and now it's clicking, I'd take him to see GP tomorrow as he's so little. It could be a coincidence but I'd make sure.