Rep Power: 0

I'm going to make a completely uneducated guess that my issue is going to be with the catalytic converter. I don't really know squat about the mechanics of my car, but I know when it's not acting "right" and I really don't want to bail on my car for new one just yet.

Here's the problem:

As soon as I turn on the car, a loud, metallic rattle will start up for a few seconds, fade away, and then come back periodically at no consistent intervals. The loudness fades in and out from being non-existent to light, to extremely loud and embarassing. This occurrs both at idle and in gear, and it doesn't seem to matter if I'm braking or not. No drops in idle RPMs, no lights on, no smoke from the exhaust, no cabin air smells. The only thing I notice from time to time happens during acceleration and it feels like there's a hiccup of a dip in power, but it could just be me feeling a bump in the road too. I'm still getting 34-38mpg.

In a panic, we rushed to the dealership and got my 01 Civic LX sedan appraised for a trade in just in case it was something major that was wrong (initial thought was a piston rod knock or piston bearing) but the mechanic there said the engine was fine, and the sound was from the braking system; all in all they were going to have to replace the timing belt, water pump, and fix the rattle which dropped the trade in value to $3k. Needless to say, we decided against a new car for now and want to go ahead and fix what's wrong.

My fiancé just checked my brake pads, rotors, calipers, clamps, and pins in the brake system. We are aware of a worn but not blown bushing on the left lower control arm, but the rattle is definitely not coming from it. We also know that the left sway bar end link is busted on one end, and will be replacing it this weekend. The stabilizer bar isn't the source of the noise, and the broken half of the link isn't hitting anything to cause a rattle, either. Motor mounts are all new in 2009, car has never leaked any fluids, and aside from being due for an oil change in the next 500 miles, and having skipped my 100K mile timing belt replacement, it's fully up to date tune-up wise. Front shocks/struts replaced in 2009; new lower control arms, right control arm in 2010.

Any clue? How would I check for sure if it's the cat? The rattle has me paranoid to the point that I don't want to drive the car.

 
Rep Power: 217

Have you checked your exhaust manifold cover? Those things rust out pretty easily, especially if you live in an area where it snows. I'd check the entire exhaust system. Loose or broken hangers/mounts. If you can pinpoint or at least narrow down the area of the noise, that'll help. This is going off the assumption it's a component of the exhaust system. The cat shouldn't make any noise if touched or moved. You could have rusty bolts on the shield of it. There's just too long a list of what it might be to be any more accurate.

 
Rep Power: 313

Yess it sounds like exhaust rattle... stupid Honda techs... What Mel is talking about happened to me with the front manifold cover. I'll show you what I mean, get your fiance to check it. Look at the bottom where the bolt goes, it's totally rotted out and was rattling away:



This is what it's supposed to look like:



Get the exhaust checked out by an exhaust shop and see what they can come up with before you go back to Honda.

 
Rep Power: 0

Problem solved. That was the rattle. Now to figure out what the hell is causing the power hiccups. :/

Thanks Mel & tbohar

The pix really helped.

 
Rep Power: 235

Have you scanned it for codes. The autoparts store will do it for free.

 
Rep Power: 313

Explain the power hiccups in more detail and we can probably guide you in the right direction there too.

 
Rep Power: 0

A year later and I should probably indicate what the issue was.

AC Compressor clutch was malfunctioning and eventually seized completely, so every time the compressor kicked on, it was putting more stress on the engine. Eventually the compressor wasn't able to turn off and the engine power issues stopped. For about a week I thought all was great.

Then the compressor burned itself out entirely and the belt started burning itself out. Disconnected the AC compressor by replacing the belt with an alternator belt for a DX w/o AC. I'm still without AC and this summer is proving to be a hot heat wave from hell, but I'm not confident enough to work on it and do all the fluid draining/recharging. Lucky for me my brother in law just finished his auto tech schooling, so I will be able to FINALLY get it fixed once and for all.