Hi all. Another task to solve in getting this car perfect. I feel like I'm coming to confession daily having posted so many times on this forum lately.
I have a whine in the rear of the car that I hear when the car is started and it increases in frequency with revs. It started recently, about 200 miles or so ago. Earlier this year and less than 1000 miles ago (it's been a busy year) I changed the gearbox oil. After reading several posts about pinion bearings going bad I thought I'd better check the gearbox oil. The plug is a slight bit sludgy but the sludge is perfectly smooth with not even the slightest hint of visible metal shavings. I strained the oil and didn't get a single metal flake.

Any other thoughts on what can cause a whine from the rear that increases in frequency as the engine revs up?

I'll be putting in new gear oil again. I believe I saw that Redline 90 was highly recommended by one of the regulars. However, I think it best to get the sound diagnosed and am looking for suggestions for someone who can tell me if this is indeed a transmission issue. Any recommendations for indy's (especially those with transmission experience) in the North Houston - Spring/The Woodlands - area? I have had a water pump replaced by European Auto Techniks and they did good work and I have read good online reviews about German Auto Center Specialists.

Thanks again, Blair

 

Sepertine belt idlers pulleys, water pump, power steering pump, alternator. They all would change with engine speed. If it's the trans it should go away with the clutch in

 

The trans bearing usually get louder with road speed, not engine revs. Look where Third-Reef suggested.

Later, Steve

 

Thanks Third-Reef and Steve. Great info. I don't remember if the sound changes when the clutch is depressed or if it changes with revs or road speed. Its out of service while I'm rebuilding the soft top hydraulics at the moment so this is a good time to change the belt and check idlers and accessories. I have a new belt to install and was holding off as the existing one has only 10K miles per the previous owner's records. Water pump is 2 years old so hope its not that.

 

you didn't say whether the rev increases happen at a standstill. that might narrow it a bit. but any of us trying to help diagnose a sound we can't hear is a dubious proposition. though many of us have heard most all sounds that failing parts make!

so, is the "whine" "gear dependent"? that *might* help narrow it down. if you did have imminent bearing(s) failure? changing out the gear oil wouldn't help, though it has never hurt.

also, a water pump failing "sound" more closely resemble the very alarming sound of a "rod knock". this is the impeller wobbling on the shaft, as it nears catastrophic failure.

belts ( as you know ) tend to "squeal" rather than "whine" lol. this is a tough game e.g. "name that noise". perhaps its the serp belt and you get lucky. so, GL w it.

 

Thanks for the thoughts. I'm travelling for the next couple of weeks so can't get it on the road to capture the symptoms. Now that I've got all this feedback, at least i know what scenarios to try

 

Hi guys, I'm finally back at this after a month of work travel and was able to get the convertible hydraulics rebuilt and back on the road. I haven't gotten the chance to remove the belt to check pulleys and accessories yet but have the following information that will hopefully help you guide me in the correct direction.

1) The whining changes with revs, not road speed (thus likely not trans bearing. Thank Christ as that sounded expensive!!!).
2) Pushing in the clutch has no effect on the whining
3) The whine is not gear dependent
4) There is no knocking sound (as 02996ttx50 noted is usually evidence of a water pump impending failure)
5) it is definitely a whine and not a squeal (as is typically associated with the serp belt)

From these clues, I'm back to Third-Reef's suggested items to check - idler pulleys, alternator and power steering pump. Is there a way to test each of these? Does each make a different noise? Would a recording of the noise help?

 

it couldn't hurt. but YT vids of "car sounds" are only one step better than written descriptions lol. although some 996 tt noises are "once heard, always remembered".

*if* ( and hopefully you do not ) have a g50 pinion bearing issue it wouldn't matter road speed vs engine revs. it's under load and in gear and to me, that noise ( audible whine & load dependent ) was immediately associated by me to my transmission, when i had a bearing fail(ing).

so if you're in gear and engine load dependent, whenever this "noise" happens let's hope it's just a belt. the PS reservoir whine of yesteryear lol ( eliminated by "clutching in" ) that used to happen before it was upgraded, no longer is a "known" issue. because it only happened to cars that were driven. so garage queens with super low mileage, may still whine! by now, every 996tt "driver" has had the part swapped out since Porsche TSB #4897 of years ago.

post an audio clip if you can, sure. i'm admittedly better at "name that tune". but perhaps others will play along.

 

When my waterpump was failing it sounded like a blown turbo. Like a woooooooooooooo with revs. Try to get it diagnosed, mine evacuated a lot of coolant after a test drive at my shop.

 

So I think I've identified the issue as the alternator. I took the car out this morning and the headlights would flicker and sometimes would not come on at all. I'm going to end this thread and search for/start one on diagnosing alternator issues. Its either a bad voltage regulator (there is a video on cleaning the cleaning the alternator and replace the regulator at $45) or bad bearings (replace the alternator at $400). Since I can't test it in the car using a multimeter, I'd like to test if there is a different way to test it.

Thanks for all your help!

 

Be careful. There are at least 2 alternators for the 996. My buddy got the "wrong one" and it caused a bunch of issues before they finally figured it out!

 

Two different ones for the same car? Interesting. For my 2004 turbo convertible, Pelican Parts shows a bunch of different rebuilts from Bosch, PPR and OEM Porsche (stupid expensive $1500). The only difference I see is the variance between 120A and 150A. Other than that I don't know what can vary on alternators. :

 

Yeah man it happened... simply word of caution to double check

His was an early car, but still. Just trying to save you the headache

 

Thanks for letting me know. I was considering buying parts before tearing mine out but I wont be doing that now.

 

You can probably still do that. Just call pelican and confirm your year and vin (or whatever they need). that's all I was suggesting.

I'd also say go ahead and pull it , take it to advanced auto parts or whatever, and have them test it for you. Pretty sure it's free and then you'll know for certain.