Thiump sound when startup

[Mickalo]

been awhile since I posted here too many other things going on but the explorer has been running great just happen to notice this now that the temps are much colder at night here.

I got a 2010 4.0 4wd xlt every once in awhile when the temps are like below 32 or so when I first start it in the morning, about 15-30secs after it starts, I hear the thump sound from under the driver side or under the hood, actually hard to tell, but then everything is fine afterwords never any type of codes or CEL lite or anything drives fine. It only does in once in awhile when colder temps outside anyone have any idea what causes this.?

TIA

 

[Rcflyer330]

Is it more like a tick than a thump? Does it have a rhythm to it? Does the noise go away when the engine is warmed up or a few seconds later?

If it is more of a ticking sound I would think it has to do with the timing chains and tensioners along with the thicker oil in colder temps.

 

[boominXplorer]

Might be a door on the hvac system sticking and finally getting enough vacuum to move. Try turning the climate control off when starting or before you park and see if it makes a difference.

 

[DavidEBSmith]

Well, we have what I would call a thump, about 10 seconds after the engine starts, feels like the passenger side. It's just long enough after starting that you just start moving and there's a thump that feels like something broke in the drivetrain. You can feel it as much as hear it. But occasionally you start the truck and look at the map or sip your coffee or something and without even moving, there's a thump. Cold or hot doesn't matter. We have a flaky blend door actuator but this feels much stronger than that.

 

[Mickalo]

thanks for the replies and info. it is definitely a thump or thud but not all the time just occasionally when the outside temps are cold usually around freezing or lower. I have check the entire drive line and suspension and found no problems vehicle drives down the road with no issues or vibration, trany shifts good, 4wd operates normally, no other noises when driving the vehicle. like this morning now it's about 35 outside started the vehicle and no noises at all it did this a few times last winter and nothing failed or caused any problems. just a weird noise from somewhere

 

[D Hook]

One thump or two? Or more?

If it's just one, I'd guess it's exhaust related. Something under tension in one position, then when getting warmed up tension is released and the part moves and thumps.

WAG

 

[Mickalo]

yea it's just a 1 thump/thud when it does happen. the exhaust makes sense that's about the only thing I can think of the may be causing the noise.

 

[Dag06XLT]

ill assume you don't have auto HVAC being an XLT, but if you have it manually set to defrost/feet it will kick on your compressor a few seconds after start up. My auto HVAC does exactly what your describe.

 

[Mickalo]

interesting you mention this I noticed yesterday and today, when first starting it up, i left the defrost/floor off and waited after the car started about 30 seconds later turned it on and no thumbs, bump or thud yesterday and today. i didn't realize the HVAC system worked this way in the cold.