Air compressor problem.

I have a weird problem. My compressor is trying to build air but it is making popping sounds and not filling my tanks.
A couple weeks ago...I had a couple mornings where I'd start the truck and it would build air fine. Then I'd hook up trailer and try air it up and it wouldn't build air. Then it would start building slowly and be fine the rest of the day.
I changed the governor and everything was good for a week.
But today I was driving down the road and i heard an intermittent sputtering sound.
Noticed it was coming from compressor area and now it won't build air pressure to my tanks and is sputtering almost constantly.
Any help for me? I'm thinking unloader?

 

Thanks....I'll check that out. Its about -30C with the wind here today so something being frozen is a definite possibility.

 

I'm starting to think that might be it. I had an air leak that I had a hard time locating. I just found it...ended up being under the insulation on an air actuated valve on my tanker. It was causing my air to drain fast enough that my compressor was kicking in fairly often.
My air dryer was on my list of things to change anyway since it's a couple years old. Guess I'll give that a shot...and make sure there's no ice in the line to the compressor at the same time.

 

Its an AD9 I believe. You need to pull the can off to get to the cartridge. Figured I'd just change the whole thing and get a new purge valve at the same time