9 Answers

Are you sure you didn't run someone over, thats the noise you get when you do.

Ducky

So, you've done that enough times to know for sure? lol

You've given too little information. A dull thud could be anything. Where does it appear to come from? Are you braking when it happens? Accelerating? Does it happen at certain speeds? Do you feel anything in the steering wheel when you hear the thud? It's really hard to say without some sort of information especially when we can not hear the thud. A mechanic will check it out and tell you what he found. He will not charge for that. You may just want to have one check it for you. 

Colleen

You will need to have a mechanic check it. There's not too much in the rear that can cause a noise like that. It could be one of your rear tires, maybe the bearings or a brake shoe sticking. I'm not a mechanic so these are just guesses based on my own backyard mechanics in working on my own vehicles over the years. Get a mechanic to listen to it. That's my best advice.

Perhaps the dull thud was you!

Two years ago my daughter (who is paranoid about noises in her car) called me and said every time she steps on the gas or brakes, she hears a thud. I told her I would check it when she gets home. Half an hour later she calls and says, never mind .... I found a frozen bottle of water in the trunk. 

It can be caused by a number of things, including something as simple as a broken band in one of your tires. It wouldn't hurt to have someone look at it though.

It can sometimes be caused by fuel in the tank sloshing when braking or cornering. If so this is a design fault in the car so not much you can do about it.

                It could be a result from the way you tend to park your car!

When i heard a dull thud whilst driving it happened to be a broken engine mount that was causing the noise, as everyone has said it could be anything.Hopefully in your case, something minor.

Open the trunk, let your Mother-n-law out.