Do these compression releases make noises when the engine is running? I was sitting in traffic next to his bike this weekend and it sounded like a water sprinkler beside me with a steady "psst-psst-psst-psst" noise that was about as rapid as a water sprinkler system.

 

No. Sounds like they aren't sealing completely which means some compression loss and probably not running quite right. I'd take them out and clean and coat with light oil and try them again. You can also buy new ones if you prefer. When you take them out look at the condition of them. They may need replaced anyway.