Hey fellow Ford Super Duty fans! I just picked up my 2008 F250 Crew Cab a few days ago. It's got 56k on the clock and a 3/36 bumper to bumper warranty on it. I absolutely LOVE the truck and have no regrets from trading in my 07 Expy Limited for it. It;s a 5.4 gasser with the Lariat package. My question stems from a weird "knocking" sound coming from what sounds like the center dashboard area. I've been trying to lock down a specific scenario that makes it happen but have as of yet not really gotten to that point. It's a noticeable "knock-knock-knock" sound that *may* be a blend door or HVAC control system that is going awry but I'm not 100% positive that that is what it is. The sound seems to come from somewhere in the center portion of the dash but it seems to be unrelated to HVAC flow position or fan speed. I do notice that the "face" vents don't always flow what they should. In order to get the "face" vents to flow I have to switch to another flow option and then come back to them. Whether this is just a weird hiccup or a possible issue with a blend door, I'm not sure. I've tried turning the HVAC system on and off while hearing the noise but it's not consistent. Sometimes the noise goes away and sometimes it doesn't...

Guess I'm just looking to see if anyone else here has had a similar issue. It *could* be something under the hood that is transmitting to the interior but I'm not quite sure at this point.

If anyone has any ideas, comments, or suggestions, I'd love to hear them.

 

Cant really help but just wanted to say congrats on the new ride

 

I have the same knock sound in my 08 SD. No idea what it is from and I can only hear it when stopped and idling. I do notice it more when it is cold out versus warm.

 

Quick update - The sound as driving me nuts this morning while I was waiting in the parking lot to pick up my youngest son from school. If I put my hand under the dash and feel the bottom of the center HVAC case, I can feel a ticking inside the case in relation to the noise. Along with the knocking noise, I can hear what sound like a servo that is running. So, I'm almost positive it's a broken or worn door servo motor or blend door motor that's having a fit.

Time to make an appt. with the dealer. Can you say "Warranty?"
This repair alone will probably make up for 1/2 what I paid for the warranty coverage. Not bad...

 

Definitely sounds like blend door(s) from your description. I've had both mine replaced under warranty. It's an expensive repair if out of warranty.

Just explain to dealer you have a continuous dull knocking sound coming from behind the dash.

 

Idling in my bosses 09 f450 lariat right now, and its doing the same thing. So it turned out to be the blend door(s) being defective?

 

Yep. Mine was a defective blend door actuator.

 

Bringing this back up from the dead...

I just picked up an '08 F-250 that has this noise, although my vent locations all function as expected. Still, I know it's not right. Has anyone done the repair on their own? There is what appears to be a servo on the passenger side just above the tranny hump that I can hear and feel humming and popping, so I know it's the culprit, but haven't found any info on replacing it yet. Thanks for any input!!

 

What ended up happening in your situation? Were you able to do the repair yourself? Having the same situation on my 07 and hoping it's not too difficult.