Rattle Noise

[dburns240]

My 91 s13 makes a kind of rattle noise at 3,500rpm's. Its weird because it only does it at exaclty 3,500rpm's any lower or higher and the noise is unheard. My guess is that it has sumpthing to do with my cat or sumpthing on the exahust but I have no idea. I have recently put on an hks high power exhaust but it is connected securly in the proper places so I really have no idea. Any ideas?

[onosqv]

Does it make that noise in every gear @ 3.5k? How about in neutral?

If not in neutral, try checking the mount that goes from transmission bracket -> exhaust. mine broke at the bushing and was causing a weird sound at lower rpms. Probably not your problem, but worth a look.

Other than that, I could only think that the exhaust is outputting a frequency that is causing something in your car to vibrate.

[dburns240]

[QUOTE=brokeAs240sx]Does it make that noise in every gear @ 3.5k? How about in neutral?

Yeh it makes it in every gear......im thinkin prob a frequency that rattles like maybe the cat or sumpthin.......dunno......puttin on a test pipe sometime this month though so i should find out if thats the prob or not. Thnx for the input.

[nismonut21]

another thing that may of happened is your flywheel bolts may have backed out due to premature down shifting..

[hek1620]

i also had this problem until this weekend. the heat shield under the car was too close to the 3 in. piping. all i did was bend it up a little. check it out.

[JDMSIL80]

I have the same problem coming for the rear, except my rattling happens exactly at 2500rpm.

[hek1620]

if its coming from the inside, it could be things that are attatched to the body. like the rear speaker racks, or the interior panels. mine(speaker rack) gets loose every couple of months or so. i guess cuz of the bass.

[Vegeta]

I know this is an old post, but your rattle problem is exactly like mine. Did you ever fix it?

I have a '91 fastback (manual) with 230,000 miles on it. I have a rattle at about 3000rpms. My heat shields used to sound just like it until I got a new custom exhaust last summer. I hate to think that my new exhaust is rattling already. I can't seem to pinpoint it. I was also thinking it may be the timing chain.

[Vegeta]

I know this is a dead thread, but I'm posting my answer anyway just in case someone does a search for it.

I fixed my rattle at 3000rpms. After thoroughly checking my exhaust and belts, I decided to check my oil. It was low and it took 2 quarts! That immediately took car of the rattle.

I didn't think to check it before because I always get my oil changed at Valvoline every three months.

During the 13 years and 230,000 miles that I've been driving my '91 240sx, It's never been low before. I can't find any signs of a leak, but I'm keeping my eye on it.