I’m trying to wring a few more years out of my 1994 Geo Prizm, and recently the engine got louder. It’s a very low end bass like sound that makes the whole car vibrate a lot more.
The muffler and resonator are relatively new, and the noise seems localized to the front of the car. What’s odd is that the engine is the loudest when it’s idle. As soon as the RPMs go above 1500, the engine is only a little louder than it normally would be. How do I find out if the problem is the exhaust manifold, or the downpipe from the manifold to the catalytic converter? Over the summer there was a brief time when coolant was leaking and dripping down onto that downpipe and burning off. That leak issue was addressed, but that downpipe has some rusty sections on it anyway.