I have an 05 pete 379 with a bxs cat.
My air dryer was making the rattlesnake sound when it would be time to signal the compressor to kick in.
The air dryer was pretty old and gummed up on the purge valve so I swapped it out, new air dryer, governor, governor line and unloader valve were changed and its still does it. Not as bad but its will still do it.
What else could cause this issue?