Strange rattle at 2400 rpm

SON240sx Automotive
1

Ok, here’s the scoop.

I drove down to Chicago last week, on a straight run, only stopping for gas and food, and the occasional bathroom break. With traffic and whatnot, it was a 9 hour drive. Let my car sit basically doing nothing for five days as I used the public transit the whole time there, and then got up to leave Saturday morning. Once again, made it back in 10 hours, with no stopping except for food/gas/bathroom; extra hour due to massive construction in Detroit.

Anyways, near the 9.5 hour mark I notice a strange sound when I shift gears. Freaking out, I pull over, take a peek under the car, and can’t see anything. I take it easy the rest of the night, never breaking the 3k mark. (During the majority of my trip I usually ran 3k, at most 3.5k to make passes on the interstate). Come home, due some research on FA and most ppl say that when they here noise they change their tranny fluid, and this usually fixes everything.

Comes Monday, I drain my fluid, and good thing too. There was at most 1.5l down there, while the FSM calls for 2.4l. That would explain the strange heat from my shifter the past few months. Refilled with some Motomaster pro stuff (forgot the name, but I’ll be upgrading to Redline in a few weeks; I needed the tranny oil in a pinch and CT was all I could find), and started driving around again. Strange rattle persists when I change gears.

Then I get an idea. :idea: What happens if I’m in neutral, revving the engine? VOILA! Strange rattle at 2400 rpm. This explains the rattle when I shift: I upshift @ 3000 rpm, and by the time I’m back in drive my car is at the 2400 mark, making a noise. This also explains why I never heard anything downshifting (as my RPM’s went up instead of down), and why I occasionally heard noises while driving w/out shifting.

Put my car up on a ramp, got under, couldn’t tell. Had my dad hold the exhaust while I revved the engine , still there.

Now, does anyone have any idea wtf this could be? I’m thinking that the 2400 rpm mark for the sound (like a metal rattle) is b/c the engine frequency for RPM’s shakes something that needs that specific frequency to make some noise. The fact that it started after 10 hours of solid driving is only fluke, I think. :? er, I hope.

Any ideas?

Cheers,
10d

2

There are a lot of heat shields around the exhaust, hit each one until you hear the noise and then rip it off or have it fix.

3

That’s what did it for me… and I noticed a lot of S13s have this problem.

DRE

4

Mines right on the 2100 mark the cat heat shield rattles.

I get under the car it doesnt seem loose at but i still stuck some folded sheet metal behinf it.
When u get my new exhause off goes the heat shield.

5

Ok, i’ve had this rattling problem as well for quite sometime now. It started in the winter, so I took the car to Canadian Tire. The guy put a clamp on the plate and said it was fixed. But it wasn’t. It still made that same annoying noise at the 2400RPM range when shifting. So, I got underneath my car, removed the clamp and removed the heat shield. This heat shield was removed not from the cat but the thing that looks like a cat right ahead of it (downpipe?:?). Would this cause the heat to cut through my floor? <-- this happened in my '90 240sx.

Anyways, this rattle is still not fixed. I checked all the other heat shields and everything seems fine. I suspect that the noise is coming from inside the cat.

Please help me get rid of this annoying noise! Thanks

6

I think I have the same problem, it sounds kinda like metal vibrating around 2200 rpm. Is it definatly the heat shield?

7

Story of the everpresent noise…

My heat shield (the one just past the exhaust manifold) was rotted, so I removed that… then I still had a rattle. Turns out my catalytic was hollowed and had a metal plate in there rattling around. Replaced… now I just have a leak around the cat (I have to braze it) and voila! no more noise…

8

removing any heat shield won’t cause any damage to the body of the car right?

9

Well i figured out the problem. The cat was gutted out and the plate in there would rattle. The dealer that I bought it from, faked the e-test. Anyways, I went ahead and bought a hi-flow magna flow cat for $100 and installed it. Now everything is running beautiful! :slight_smile:

10

The rattle could be your rod bearings as well. That’s what it is on my SOHC but I’ll be swaping a DOHC in very soon just haven’t driven it in awhile.

11

Rod bearing rattle is different then what is described. My old SOHC had that and it sounded like the timing chain guide.

Now the only ratting I get is from the two halves of my exhaust hitting together when the beast backfires…

:twisted: