I have 2004 Ford Explorer with a thumping feel and sound. When I drive over 50 mph and let it coast, the thumping starts. I feels as if it's coming from the back but not sure. The check engine light is not on. This started happening when I had all the fluids changed. I've had the tires checked and are ok. The transmission shifts gears just fine. It has 128,000 miles and drives fine except that thumping noise. It feels like I'm driving over bumps in the road then goes away if I push on the brakes or gets under 40mph. Please help. Very frustrating.

I'm not sure what you mean by "Thumping". Please explain if this thumping is engine or body related. Try to describe the symptoms with more detail. Thumping to me, could refer to a Random Misfire, Internal transmission failure, Using the 4WD while on the wrong road surface or the tires are not all the same size, a defective U-joint (in the drive-shaft), a defect inside the rear drive-axle (ring&pinion), maybe a defect in a tire (not balanced or a bubble in the side-wall or tread), wheel bearing, ball-joint, tie-rod, or a needed alignment (observe if the vehicle pulls to one side and look for irregular tire wear). Let me know, good luck.

Sounds likes trans problem common to the Explorer, try changing the transmission fluid (mercon V) and add an anti-shudder additive. Does it happen mostly between 45-60 mph?

Check the radius arm bushings or the lower balljoint .

most def you need an alignment and you also need to check inner outer tie rod end and check the tires belt as well

If it only did it once then it was a road problem most likely and not the car.

if it is the pinion bearing located near the drive shaft it could cause slack and thump the drive shaft. with the truck jacked up the driveshaft would be sloppy near the rear up and down.

You could have a bad tire, if the truck sat for a long period of time. You may also have a belt separation in the tread of the tire.

check for any boot rips on the axles, check rubber seals on tie-rod ends. Check shock absorbers to see if the shields are vibrating.

sound like worn cv joints.

Maybe check for loose u-joints, transmission mount, or carrier bearing if you have a two piece driveshaft.