Question about a 2004 Saturn Ion

Hi everyone I’m new to the forums and I have a question about a car.

My girlfriend’s step-dad’s 2004 Saturn Ion has developed a knocking sound that you can feel under your feet. You can feel this best in the front passenger seat, however it also seems to emanate from the back of the car as well.

This car is a manual transmission with at least 120,000 miles on it. It only seems to have this knocking sound in the cold weather and other than that there have been no major problems with the car.

One more thing that I feel worthy to note about the car is that it is a daily driver that commutes about 70 miles a day, from pretty much one side of New Jersey to the other (from border of PA to the train station in Newark to a job in NY). If it’s not going there it’s going about 45 miles into PA, so it’s pretty much constantly being driven.

As a reasonable guess, I’d say you have a loose muffler. You need to crawl under and give the exhaust pipe a vigorous shake to see if there is enough free play in the exhaust system to create the thumping that you feel and hear.

Is this rhythmic, and if so, does it vary with car speed? If not rhythmic, is it doing it in turns or on the straight?

Thanks for the responses. It is not rhythmic nor does it vary with the car speed. However it does not happen when the car is stopped or at idle. I won’t have the chance to see the car until Sat when we go to visit, I will take a look at the muffler then, thanks for the idea :).