S Duo Millia

Recently, and quite suddenly my S (2007 77K miles) has developed a sort of chirping/whining sound when at partial loads. I.e. just between accelerating and decelerating and at constant low to medium speeds. It behaves much the same as the bad diff in my FB RX-7 (although its run fine like that for ages, even with close to 270hp). Since the cars share ring and pinion gears it doesn't seem too much of a leap that similar symptoms could mean similar things.

Only changes I have recently made are a HKS 75mm single, Mugen header and 70mm test pipe although these have caused me no issues for over 2000 miles.

I currently have the car up on jackstands and I have checked the exhaust, can't find anything out of the ordinary. I have played with the rear wheels and can't find anything that would indicate wheel bearing issues (I have done the hub nut torque adjustment about 10000 miles ago). I have been under the car and rotated the wheels and drive shaft/axles and I am pretty sure everything feels as it has before (I have done routine checks while under the car before). Does seem to be some play where the axles enter the diff, I am not sure if this is normal, maybe it is the bearings in the diff. It does seem to sound like a bearing, however as I have said it is intermittent and only when transitioning from acceleration to deceleration or driving in mid range rpm at constant medium speeds. It chirps in and out as the load changes and I can feel it through the car/pedals.

I recently changed the tires maybe 1000 miles ago and they said my wheels were somewhat bent but they managed to get an OK balance, recommended I get them straightened which I have yet to get around too, not sure if it's related. Car felt great after tire change and I never noticed any vibrations before.

I have a mechanical warranty (aftermarket) so I could just take it in, but I always like to know what is wrong before I get any work done on my vehicles, it would also save time as this is my daily driver.

Anyone have any ideas what it is or what to check to properly diagnose this? I am getting diff oil tomorrow so I can change it and check for filings etc.

TerminatioN

Didn't change your clutch recently did you? Sounds a lot like the "clutch buzz" issue some AP1s had... which is unlikely on an AP2 and also would have been there all along and not just started suddenly, but its possible a shop could have put new old stock parts (that had that problem) on the car if you had the clutch done recently...

MR.T

I've had a bad u-joint in a drive shaft that made a chirping sound, though the s2k shaft is completely different you still may want to take a look in that area.

You could always drop the diff fluid to see if any damage is sticking to the magnet.

Those noises are hard to track, good luck with it.

S Duo Millia

Nope the clutch hasn't been changed since I have owned the car, doesn't seem like clutch buzz from the symptoms I have read. Haven't got a chance to change the diff fluid yet, been so busy at work, will probably only get to it this weekend.

S Duo Millia

An update on this, the noise is engine RPM based, if I take it out of gear and put it in neutral while cruising it goes away. And if I rev it to 3.8-4.2k the noise/vibration will happen on and off and seems to get worse when I depress the clutch. This leads me to believe it is clutch based, but seems nothing like clutch buzz, I am at a bit of a loss. I am going to triple check the exhaust when I get a chance, it seems to happen in the drone range of the exhaust so could be causing a resonance or a rattle of some sort in the exhaust, maybe something is loose or rubbing.