Bendix Air Dryer "Ticking" 2008 ProStar

[Waterloo]

Hey guys, a few weeks ago my air dryer started ticking. I replaced the cartridge when I serviced the truck at my local TA the other day. The old cartridge was pretty messy. I change them out annually as I normally don't drive much more than 70,000 miles a year and rarely idle. Just surprised how gummed up looking she was.

But anyhow, she is still ticking, and this being kind of an odd ball air dryer unit, what do you think it is? I cannot get under there to inspect as the truck sits to low, air dryer is stuffed up under the cab on the inside of the frame rail under the cab. Stupid location... I'm thinking purge valve? Any thoughts? Still operating normally, just ticking...