Car is making a weird noise

thanimations

I'm pretty car stupid, so this might be a no brainer for some of you. My car has been making a weird almost-rattling noise when I'm going 45-50 mph. It doesn't make the noise at any other time or condition, not when I'm going much faster or on the highway, not when I'm accelerating (fast or slow), not when I'm de-accelerating, not when I'm braking. Only when I'm cruising at the 45-50 mph range. I'm good at 40, and I'm good at 55 or 60.

The sound is kind of like a rattling, but also kind of like a loud fan, so I thought maybe it was just vibrations, but the sound cuts out the second I either push harder on the gas or lay off of it. It's just when I'm maintaining 45-50 mph.

My car is 2003 Infiniti G35, automatic transmission, if that's relevant. If anyone has any ideas before I take it to a shop, it would be greatly appreciated.

Sir Carcass

It might be spark knock. Does the car recommend premium but you use regular?

Spudge

It could be vibration specific to that RPM - some cars (Volkswagens) have this problem a lot and it could be something similar in your G. Check the bolts on your exhaust manifold heat shield are tightened

Also check and see what RPMs you're running at at 45-50 mph. Try to hold those RPMs in a different gear (or while sitting in neutral) to see if the noise occurs then as well

Darkewolfe

Could be your tire alignment, too. Sometimes a slightly off alignment will cause vibrations at a specific speed.

IronKnuckle's Ghost

Darkewolfe wrote: »

Could be your tire alignment, too. Sometimes a slightly off alignment will cause vibrations at a specific speed.

My money's on this, but you should check the air pressure in your tires to make sure it's in spec with the recommendation on your driver's door. Also may want to ensure that you haven't lost one of the wheel weights.

thanimations

Hmm the tire alignment might be it. I did just get the tires changed, so I'll check that first.

KryptykSol

if the steering wheel shakes its probably wheel balance (not alignment, alignment wont cause shakes, it will cause the car to pull in one direction or the other, or have very strange steering feel) if the steering wheel doesnt shake, my bets are on a wiggly heat-shield on the exhaust.

Does it make the same noise if you rev the car in neutral to the same RPM that it is at when you are driving and hear the noise? That would eliminate wheel balance issues.

Edit: my bad, just skimmed the thread, Spudge beat me to it

thanimations

Nope, no wheel shaking. And the noise seems much more vehicle speed dependent.

Spudge

Well vehicle speed means a moving part issue. However the only moving parts that hit specific RPMs (and thus specific frequencies) only during that speed are

Transmission (yes it hits those RPMs in different gears, though if you've tested holding other gears at the same RPM with no vibrations you could probably count it out)
Rear differential
Driveshaft
Axles/CV joints
Wheels/brake rotors/hubs

If the sound started after you had fresh tires put on, check your lug nuts and brakes. I'm not sure if your car has them but if you have floating discs they can cause vibrations if they were accidentally messed with when R&Ring the wheels

Zeon

The new tires could just be noisier than your old ones. Some tires absolutely drone at certain speeds. If its not that, id guess a wheel balance issue or its out of alignment, those are generally the issues when you get a drone or a shake at a certain speed (but free from issues at all other speeds).

EWom

I have a used blazer that was abused by the previous owner, and it does that shit all the time. There are 3 sounds. A weird rattling as you describe that only comes about in specific conditions, as you describe (mines usually 55mph). An unbalanced washer sound, that usually starts at about 45 and gets worse as I go faster. And an almost grinding sound.

The culprit is always one of 3 things. Alignment, Wheel Bearings or the worst one, I can't remember th eexact name, but its fuckass expensive to fix and has to do with the axle, and how it connects to other stuff.

I say take it to a tire/wheel specialty place, they generally have better rates than a regular mechanic for these things, at least form my experience. Tire Rama, les schwab, etc.

thanimations

Thanks, everyone for the insight. I'm going to take it into a wheel place this weekend, so hopefully it just needs to be aligned.