How can you tell if noise is dirt or static?

I've been listening to a lot of LPs lately, and the weather has been dry so I have a humidifer running all day long. However, some records (older ones) that I've picked up used still have a lot of ticks and pops. How do you know if the issue is being caused by a static charge on the vinyl, or if it's dirt that is still in the grooves? I've cleaned all records using a Spin-Clean, but I plan on picking up a steam cleaning unit today to give that a try....