Rear Air strange noise on 2010 V8 4x4

[geosnooker2000]

I have been enjoying my new ride I got back in February. A few minor defects I would like to rectify, but all in all, a solid truck.

Something started a few days ago that has got me worried. At first it sounded like a half-filled gas tank sloshing. Then I noticed that... no.... I have a full tank. I turned off the rear air blower to listen more closely, and the noise stopped. Turned the rear air back on, and it started again The frequency is about one sound (slosh) every second or slightly longer, but not as long as 2 full seconds. Probably less than a second and a half. Since I bought this without a proper manual, I don't even know if there is a separate evaporator coil in the back, or is it just ducting? I doubt it is just ducting from the front to tell the truth.

Any insight into how this system works and what could be the cause of that noise would be greatly appreciated!
George

 

[07EddyB]

Look underneath and you will see refrigerant and coolant lines running to the back. You have a heater core and a evap coil back there. Just FYI. I can't explain a sloshing sound.

 

[geosnooker2000]

Original post over a year ago. I just noticed it again, and forgot I had posted this question last Summer. It is still doing the same thing, but I hadn't turned my rear air on since last year until now. Just a renewed request to anyone who would know what that thumping noise is over my left shoulder behind me when the rear A/C is on, and is it anything to worry about.