If it's a type of clunking noise, check your gearbox. If it's some kind of rattling, check your hubcaps.
Dynamat
It's $7 from Honda dealer. Called, I think a door stop. I just bought one. They are shipping it to me for a total of $12.
My 1997 Honda CRV is making a rattling noise when driving in rough roads
The rattling sound in the front of a 1995 Honda Civic wheels can be caused by wheel bearings. These bearing allow the wheel to turn and when they fail the produce a loud noise.
balance it
Dynamat usually does the trick, also try removing the trunk liner and seeing if anything is vibrating noticeably inside it. http://www.dynamat.com/
Which hubcaps are you talking about? Please rephrase this question!
I went to buy new hubcaps for my car.
The heat shield on top of the converter may have broken loose. it can be repaired. If the rattling is inside the converter it must be replaced.
The best way to stop the rear brakes on a Mazda 626 from rattling would be to replace them. New brakes can cost between $20 and upwards of $100 depending on the quality of the brakes.
Replace it.Replace it.