Former 986 2.7 owner, new to me 996TT. My TT's engine sounds sort of harsh compared to my 986 2.7L. I know it's a different engine, but I'm wondering if there is something amiss with the turbo.

It's not too bad, but I hear:

1) at idle there is something that my untrained ears think is tappet noise from the driver's side of the engine. Not too much, just something that I don't hear from the passenger's side, frequency of the "tappet noise" is proportional to engine rpm. This noise is overcome by the general engine noise not much after idle so I can't hear it after 2000 rpm
2) revs fairly smooth between 0 and 3000rpm
3) harshness between 3000-4000rpm
4) less harshness 4000-redline but still some harshness

I'm sure you'll want to know what I mean by "harshness". I can't describe it other other than it's a slightly unpleasant mechanical noise that should not be in character with an expensive engine.

Two comments/questions:

1) could it be either a worn alternator or water pump? My Boxster had a worn shaft on its alternator and I believe it's a similar if not exactly the same Bosch part. The Boxster's worn alternator shaft made more of a racket that this however. Also I've heard that the water pump is a weak one on the Porsches. And a worn water pump on my old Honda made a racket too, again, louder than this but maybe the Honda's was on its last legs.

2) I occasionally hear a rattle when shutting off the engine. I'm thinking something is loose in the exhaust system. Maybe a heat shield. Again, the driver's side (I think; this one I'm not so sure about). Could this be related to the harshness? I'm taking it in to a local muffler shop as I'm thinking they are familiar with exhaust systems and it wouldn't cost anything for them to put it on a hoist and look. The rattle is intermittent and I can't always duplicate it. More often than not, the engine shuts off with that wonderful deep burble that I expect; just annoyed that 30% of the time, there's a cheap rattle sound instead!

3) Could it actually be tappets or something similar inside the engine? External bits like the alternator or water pump I can deal with. Taking out the engine and opening it up won't be something I can do and should be very expensive.

I have looked through the threads while researching the purchase and don't recall this type of symptom. My understanding is that these are robust engines. Any comments / advice is welcome.

 

Does the rattle noise go away, at idle, when you press the clutch pedal in?

 

There is no rattle at idle. The rattle manifests itself only when shutting off the engine and only 30% of the time at that.

The "tappet noise" is not the rattle I was referring to. This "tappet noise", unlike the rattle, *is* usually heard when idling. It's not a loud noise. It's at a level that I *just* notice it. Maybe this is normal for our engines. I'm not sure. I will check to see if what I believe to be a tappet-like noise goes away when I depress the clutch.

 

The metal timing chain has a "rattling" sound at idle. Sounds pretty normal.

 

NineFiveOne: Rattle is still there even if clutch is depressed (curious, why do you ask? Something related to the clutch causes a rattle?)

Ari: I'm encouraged to hear that it might be timing chain noise, but my untrained mind thinks that timing chain noise might be higher in frequency. What I call "tappet noise" at idle is a bit of a "heavier" sound than what I think timing chain noise might sound like, but admittedly I don't know what timing chain noise sounds like.

 

The idling tappet noise is normal. The other one is not. Could be vibrational resonance from something, maybe the same thing that rattles when you turn off the engine. I don't think it is the engine. I just had a mystery noise that was diagnosed as a bad power steering pump. After changing it, the noise was the same. Turned out to be a pulley bearing for the serpentine belt.

 

The transmission will make noise that I have heard on a number of cars. When you press the clutch in, all the gears in the trans stop moving and the noise would go away. At least you dont have to worrry about the trans.

Besides that, these cars do make lots of tappet noises, your 986 should have made that same sort of noise though. Like landjet said, it could be a idler pulley. Could you take video so we can hear it?

 

it seems the nuts rattling around in a can is normal lol.... unfortunately the 3.6 turbo motor makes annoying noises (ticking rattling) well at least the dozen or so i have been around... the sound you here at shut off is most likely a heat shield, does it have an aftermarket exhaust?
tim

 

I'm glad to hear that some tappet-like noise around at idle is ok.

The shut-off rattle does sound like a heat-shield type of sound (something loose anyways) and which I hope the muffler shop can find and tighten a bolt to fix. The exhaust is stock and so should not be contributing to the rattle (unless the muffler is loose).

I am more concerned about that 3-4000 rpm harshness. I think it could be some combination of:

1) idler pulleys and tensioners, like with Landjet's car (I replaced these on the 986 along with the alternator and the associated harshness in the 986 went away)

2) alternator

3) water pump (a known weak part with Porsches?)

The above items are inexpensive enough that I'm thinking of treating them as maintenance items and just replace all of them (and the serpentine belt) during the 996TT's winter hibernation. Do people do that, i.e. just replace these external bits in case they wear out? Mileage is at 56,000 mi and it's an 02 and so maybe it's just time to do those things.

Anything else I should replace while I've got everything apart in that area of the engine? Thermostat? Various hoses?

 

harshness between 3k and 4k and rattle when shutting off is kinda concerning. I have never had that and I have been through stock tune, and two more tunes never having experienced that. I have been around plenty of turbos being shut down and not experienced that and have driven in plenty of turbos through the 3k-4k range and not experienced that roughness.

Does the rattle exist regardless if you are cruising lightly in the 3k-4k range or does it occur only at WOT? Does it worsen in any conditions? Does your car have tune, LWFW, aftermarket clutch, etc.?

Check your motor mounts if loose or broken. Probably ok, but rattle means something loose or off balance, rough running is usually fuel or timing. Not always. I have experienced these conditions with other cars, but have no clue how these cars act under these circumstances.

but definitely don't take it lightly. a vibration can end up causing serious damage later on.

Good luck with it. Hope you can figure it out soon.

 

I'm now of the belief that it's a bad bearing on one or more of the items driven by the serpentine belt. I had someone rev the engine while I stood at the back with the hood(?) open and yes, what an ungodly racket! No wonder it sounded harsh from the ****pit! [And why didn't I think to open the hood and listen earlier? --probably because as a former 986 owner, "opening the hood" was a bit more fiddly]

I think it's one or more of alternator, water pump, tensioner, or the 2 pulleys. The 986 had a bad alternator and one pulleys or tensioner; sounded sort of similar (louder because engine was mere inches from me, but more muffled socked away in its mid-engine location). Replacing those restored its smoothness, and I'm thinking it'll do the same for the 996TT.

I'm planning to replace all those things above now, including the belt, just because it's getting close to the 60K miles mark and I want to get a fresh start for my new-to-me 996TT.

 

I disagree. The sound you hear occasionally at shufoff is the OEM dual mass flywheel.

 

it might be a good idea to take it to a good porsche mechanic for a second opinion before replacing all those parts

 

If it is not one of the pulleys the tapping noise you hear at idle is most likely the intermediate shaft.Most all of them do it and some worse than others.Mine did it when it was brand new.Many motors have been replaced under warranty because of it but only when they get excessively loud.I wouldn't worry about it unless it is really bad(loud) .If it is loud and deemed to be the intermediate shaft unfortunately the motor will need a rebuild.Put the car on a lift and check for the rattle when shutting off,hopefully it is something minor.Pull one of the plugs if you are experiencing harshness at 3-4k and check their condition.They need to be changed at about 15k regardless what the manual says on a stock car and 10k if modded.Good Luck!