Hello this whirring noise is coming from the rear end of my MY00. This car has a Ap2 diff and axles installed from the previous owner idk when. Car has 165k miles. Recently all the bearings on the car were changed and new diff fluid was changed about a month ago. Car hasn’t been touched besides being daily driven. The sound occurs at 20 mph+ and keeps going even when the car is coasting in neutral. Any ideas what this could be and solutions? See video, near the end I put my phone closer to the rear to hear the sound better.

https://youtu.be/WceBjWsWs8o
Thanks

 

When did the noise start? After changing something, changing fluid, or has it always done it since you've had the car?

 

What "new diff oil" was used? Won't hurt to drain it, check the magnet on the plug, and refill with proper spec hypoid gear oil regardless of what's in there now. Messy but not expensive.

-- Chuck

 

started just last week. I changed the diff fluid about a month ago though..

 

I used amsoil severe gear 75w-110

 

Should be good to go on the differential oil. Amsoil severe gear 75w-110 meets spec (SAE 90 GL5).

The SAE 90 spec changed since our cars were built and that oil is in the bottom half of the "old SAE 90." 75W-140 also meets the "upper half" of the old spec so it can be used if you want to try it. A bit "thicker.". Spec is spec.

I'm guessing I have Amsoil severe gear 75w-110 in my differential at present 'cuz there's a partial bottle in my garage next to a couple unopened bottles of Lubrication Engineering 75W-140. I change the differential oil when I change the oil filter -- every other oil change.

No noises in my car but I have 100,000 less miles on it.

A glance at the drain plug will show if anything is wearing. You only need a couple of ounces to send to Blackstone Laboratories in Indiana for an analysis which will identify metals, etc. If you need the sample bottle Email them and they'll send a postage paid bottle and mailer to you. Will answer a lot of questions even if it finds no metallic wear.

-- Chuck

 

Could be transmission secondary output shaft -- tends to experience galling on the bearings, causing a speed-dependent whirr/whine. Long-known issue, as the date of the following thread shows:
https://www.s2ki.com/forums/s2000-un...-noise-409603/

Bad news: there's no cure short of R&R-ing the shaft/bearings. Good news: it's mostly harmless if you stay on top of fluid changes, and you eventually get used to the car sounding like it's always in reverse.

 

Do you know how I could diagnose this to be the case? The differential was swapped out by the previous owner at idk what miles but it was swapped for an AP2’s

 

^Put it on jackstands, have partner start and run it in gear at low rpms (to minimize noise) while you listen from under the car. It'll be pretty clear whether the noise is coming from the gearbox or the diff.