My '02 4dr 4wd has a thump noise when going over little road bumps at slow speeds and it sounds like something is loose inside the air duct. I have removed the glovebox lid and checked everything I could get my hand onto...but found nothing loose. I even removed the temp door actuator to make sure the temp door was not broken...it was not...moved freely.

So I am wondering if it is the heater core moving around and was hoping that someone has a picture that shows what holds the heater core in position.

Or does anyone have another idea as to what it could be? It is not suspension or drivetrain related...at least that I can find.

Appreciate any leads to pictures.

 

the heater core is held in the plenum box with several screws on top of a removable panel.

the plenum box is held to the firewall in the cab at the bottom. just under the carpet on the pass side is three bolts. on the outside it is held in place by one bolt that is hidden inside the blower motor housing..also a fastener about middle of the fire wall above the distributor (that one is hard to get to as well)

has anything fallen into the ducts?

is your floor damper working? they can break off and become loose. the first sign is if you have issues getting air movement to the floor vents.
i would check each position on the hvac selector and make sure all your dampers are in place and working.

hope that helps.

 

All vents seem to work as they should....heat to the floor and defrost...cool to the dash and defrost.
Nothing has been dropped into the air duct.
I have had the front dash cover off and looked into each vent opening...nothing but dust.

I will check to see if any of the bolts holding the air box are loose/missing.

Thanks for the info....I will keep looking.

 

Well forget what I originally wrote; the noise just appears to be coming within the air duct, but it is not.
Thinking back and talking with my wife, the noise began after I had replaced the lower ball joints, outer tie rod ends, driver's side axle and the sway bar links.

After I did all of this work I noticed that the Blazer was not level when looking at the front from a distance. I made some measurements and end-up reducing the twist on the passenger side T-bar to lower the left side a bit. Not much...maybe half a turn, dropped the right side about 3/8" is all.

Well today I checked all the ball joint bolts on the passenger side...all tight. When I raised the front end using a floor jack that was in the center of the front crossmember, I noticed that the right side came off the driveway much sooner than the left side....do not know why. But I decided to loosen the sway bar bolts as they seemed to be too tight and compressing the bushings too much. Then I decided to give the passenger side T-bar about a 1/2 turn tigher; the right measured a tad-bit lower than the left side.

Went for a drive and could not get the thumping noise to return going over my test road.
So apparently the noise was caused by either the T-bar or the sway bar links..not sure which. Maybe the T-bar was becoming unloaded or something....or perhaps the sway bar links were contacting the frame somewhere....just do not know.

I need to continue to drive it and listen.

 

well glad to hear you may have found it.
hunting for noises is a real p.i.t.a. sometimes

 

SPOKE TOO SOON.....

Noise is unchanged; found a washboard road this morning....yep noise is still there...unchanged....

I guess the only way I am going to find this is to remove the entire dash and then go for a drive. Not something I am looking forward to...but out of other ideas.

Oh well.....such is life.