Hi all,

07 Altima SE. I'm experiencing a lopey sound when driving slow (under 5mph) when warm only. Kind of a wah wah wah sound. Drives smooth and quiet the rest of the time. Can find no exhaust leak or intake leak. No codes either. The sound seems to coincide with engine speed not wheel speed. Any suggestions? Thanks.

The only things that generally make noises like that are bearings, and possibly the Torque Converter. If it's "buzzy" you can add the timing chain guides to the list. Since the water pump on the 3.5 is chain-driven, you can eliminate anything on the belt by removing it and briefly driving the car. If the noise disappears then you know the source is something on the belt, P/S, alternator, A/C clutch or one of the idlers. If not, worn guides or a bad water pump should be audible with a stethoscope on the front cover even if you can't hear it at idle with naked ears. Same thing for the Torque Converter, you should be able to hear it with a steth on the bellhousing (although you'll need an assistant to put the car in gear with the brake on).

I really need to get a stethoscope. It's not very noisy, my wife can't hear it. I notice it only once the engine is hot and driving through a parking lot or something. Could weak fuel injectors or spark cause something like that too? Thanks for the suggestions I will look into those things you mentioned.

Actually, if it's faint and only does it warm, you might be hearing the stepper in the CVT or a bit of whine from the diff. Diff noise can change with load at parking lot speeds and can sound like it's engine-related. The diff shares fluid with the trans, has it been changed lately?

PS - $5
https://www.harborfreight.com/mechanics ... 63691.html

I have drain and filled twice, is now at 65000 miles. Used Nissan ns2.

VStar650CL wrote: ↑

Sat May 07, 2022 8:43 am

Actually, if it's faint and only does it warm, you might be hearing the stepper in the CVT or a bit of whine from the diff. Diff noise can change with load at parking lot speeds and can sound like it's engine-related. The diff shares fluid with the trans, has it been changed lately?

Do you mean it can change with engine load? Would that be cause for concern?

No, it's more because the car's inertia is small at parking lot speeds and it can cause uneven rolling resistance, which gets absorbed by the torque converter like a hydraulic rubber band against the spinning engine. Because the car's speed isn't changing, it can seem like the noise is related to the engine and not the diff, even though it's actually the diff gears that are experiencing the uneven load. It doesn't generally mean anything.

Thanks for the explanation! It sure sounds like that's what could be happening here. I haven't noticed it getting worse, just noticeable at times. Is the CVT more prone to this? Haven't noticed it in other autos I don't think.

Yah, the CVT diffs use tranny fluid and not hypoid like a rear diff, so the gears don't have as much cushion and it isn't unusual for them to make a bit more noise. The steppers can be whiny or buzzy too, but neither noise is usually loud enough to hear with the windows closed and most people never notice them.

Awesome, thank you VStar!

You're most welcome. Happy motoring!