Intercostals generally don't cause pain for no particular reason but they can go into spasm because larger muscles are pulling them out of alignment. The weird thing about our bodies is that a lot of muscles have only motor nerves, not sensory nerves so we are unaware of it until the joints or attachments start complaining. Can you see a physio about loosening up your serratus anterior muscles? Those are big culprits in intercostal pain and spasm