A few days ago my 2000 Dodge pickup started making a loud rattling noise once I get to about 75 mph. This has never happen before. It has about 125K but is well maintained. Any ideas?
Where does the noise seem to be coming from?
Heat shield? Do you have some vibration?
The only way this will get solved is under the vehicle. If you do yuor wone work, put the vehicle safely on ramps, slide under, and start ahaking things. If not, simply bring it to your mechanic. These kind of resonant rattles are generally easy to find and fix. Based on the age of your vehicle there’s a good chance its a loose heatshield on a cat converter. These are cheap and easy to permanently secure with a worm-type hose clamp from the hardware store.
it seems to be coming from the front, under the drivers seat but I may be wrong. Also, I did just get an alinment and tire rotation and balance. Don’t know if that matters
It does matter since you eliminate tires (not likely your problem anyway) and worn front-end parts as the cause. No mechanic worth anything would do an alignment without first inspecting the front-end. Nor would the alignment last very long.
But, if along with the rattling you have a vibration or if the car wants to pull to one side or the other, maybe your mechanic or tire-chain store is just that, worthless. If either of these conditions exist, get the car into a better shop and find out what is going on.
If not, I agree that this is just a loose heat-shield or something, which should be secured or replaced.
In case anyone was curious I think the mystery is solved. It seems my drive shaft was bent a bit during replacement of the U-joints, hence the vibration and noise. I appreciate the suggestions.