the truck now makes a whining sound for about 30-40 seconds on a cold startup from the fuel tank and def tank area . what could this be ?
its at the dealer for other issues also , the dealer said that it was my starter making the noise, I'm pretty sure the starter is attached to the motor and not located by the fuel tank lol.

 

Don't these trucks pump the DEF out of the lines and back into the tank on shutdown? Then, on startup, it pumps it back into the lines? I could be wrong, but that's the way I thought it worked, and could be what you are hearing.

 

On cold startup, its probably your frame mounted low pressure fuel pump. How many miles on your current fuel filters? Might be time to change them?

 

I had no idea that the def tank did that each time , I thought it was only used when cleaning,

I have 117,000 on the truck and the filters are only 2 months old, I wonder how easy that pump will be to replace

 

4 bolts and some wire connectors.

 

On my 2011 the DFCM (fuel pump), located on the driver's side forward of the fuel tank, would whine on start-up. This was more evident in colder weather, and especially if I used remote start and was outside the truck. Sometimes I could hear it from within the house. I changed fuel filters (with new lubricated o-rings) every 15,000 miles for the 4 years I owned that truck and the sound was never abated. I hear it ever so slightly on my new 2016, but then I also know where and when to expect the sound. Some have speculated that it is air being purged as the pump primes for start-up, but when you change your fuel filter and cycle the key 6 times, you can hear the gurgling sound made by air being cleared out. To me it always just sounded like the fuel pump providing pressure, an action I wouldn't expect to be silent. I would assume over time that as parts wear and tolerances increase it might become louder, I have no idea why cold weather above freezing would have the effect it does. I do think it's a normal sound, though.

 

The sound from the DEF tank purging the lines is most evident on shut down. I wouldn't think the DEF would be pumped back into the lines after star-up until it was time for a dosing event in the exhaust.

 

The DEF line purge on shutdown (don't know about a refill on start-up) only lasts for 5 seconds or so, but if you turn the ignition key to on without starting the truck the fuel pump will run for exactly 30 seconds then stop. Hope that might be helpful in your diagnostics.

 

I have the truck back from the dealer, it went in for a new sunroof track, no A/C and the whinging sound from the fuel tank area. The sunroof is fixed , the A/C was recharged and they couldn't find the leak, guess what no A/C again 1 day later. the whinging sound they said was the starter motor , for the life of me i cant understand that but they replaced the starter and the sound is gone , figure that one out i cant. Back to the dealer again this week I so hate the HVAC system in this truck its been a pain in the *** from day one.