Paranormal investigation books like the X-Files?

I'd love to find a book or series that reminds me of the X-Files. Specifically about a paranormal investigator(s) who solves cases involving aliens, cryptids, superhuman abilities, and government conspiracies. I'd love something that also matches the general tone of the show. Somewhat dark, but doesn't take itself too seriously and with a little humor sprinkled in. I'm not huge into vampires, werewolves, magic, or high fantasy. I'd prefer something more on the sci-fi side than the fantasy side. Thanks in advance! 🙂