AdmiralB

I've got a new CTS-V that has a rattle at low speed/low RPM. I noticed it immediately at delivery, the salesman heard it, and I've had it into service - no problem duplicating it, but GM told them "It's normal".

I've owned a '99 LS1 Camaro, an '04 Z06, and I currently own a 427 convertible. None of them make/made this sound, nor did the ZL1 Camaros I test-drove before buying the Cad.

It sounds like sheet metal rattling, like a shield of some sort, but it's definitely coming from the clutch/flywheel area. It'll do it almost universally at takeoffs from a rest unless I really hit the gas and slip the clutch. It'll also do it if I'm idling in first or second, say in a parking lot, and start to accelerate.

It makes no noise in neutral, it's only when torque is being applied.

Ideas?

Forcepower

iTrader: (23)

Is it a rattle or a chatter? Stock or aftermarket clutch?

AdmiralB

It's a rattle. It does it with the clutch fully engaged.

Totally stock. Two months old, ~2000 miles, but it's done it since delivery.

GM just sent the dealer the stock "High performance vehicles make more gear noise" TSB, and told them it's normal. I think the dealer's interested in making it right - they don't think it's correct either - but GM won't authorize them to do anything and they'd be shooting blind without guidance. It's probably the only manual CTS-V they've sold, although they've probably sold a few manual ZL1s.

Forcepower

iTrader: (23)

its a t56 and a rattle is not normal.... I would push for them to fix it and make it right.

jmd

iTrader: (4)

It's unlikely to be the trans. itself. It could be the clutch.
NVH is tricky to diagnose in some cases.

Since "we're going to wear you down until you're out of warranty instead of putting hours into diagnosis" is a savvy business model . . .

Put the car on stands and disconnect the driveshaft from the tripod yoke. Start it up and see if the problem re-occurs. If yes, you've eliminated the driveline. Why do I suggest that first? Because of GTO guys who think their T56 is rattling when they bring it to me.

From there, stick a hose in your ear, and against components until you find it. Or wait for the dealer to work their magic.

AdmiralB

I appreciate the suggestion. It really sounds like something in the exhaust rattling, but except for the junction at the rear cats (which I've checked), the system is one-piece.

I'd be surprised if it makes the noise with the shaft disconnected, though, since it seems to need some 'load' on the system to do it. In any case, I won't be doing any experimentation until the temperature rises, preferably above zero. It's a two-piece driveshaft, and I intend to check the carrier housing, although I'm 90% sure the sound is coming from a place forward of that.

It seems weirdest to me that it makes the noise when I take off 'normally', from a stop, but if I give it what I would call excessive gas and slip the clutch a little, it's totally quiet. That makes it seem like a clutch issue to me.

But since it also does it from a roll, with the clutch fully engaged...I don't get it.

AdmiralB

In the interest of resurrection - and saving my sanity - I've been at the problem for the last month, with minor success.

After putting it on stands and judicious tapping with a rubber mallet, I discovered the exhaust didn't mount correctly. The junctions aren't flat 'butt joints', they're cones, and the assembly didn't quite line up with the head pipes. It rattled - a lot. The dealer replaced the exhaust, and...it still rattled, but rather differently.

I then discovered that one of the new mufflers rattled - you could look in the tailpipe and see that the output pipe would move around if you pulled on the tail. So I tack-welded that together (could *just* get a rod down in the muffler), and the rattle...subsided a lot.

But it's still there, more than it should be. So, back on stands...and I started it up, put it in 6th, and had my son pulse the gas while I went under on a creeper. And it's coming from the bellhousing/trans. The transmission really sounds like it's full of rocks.

Since GM has already said that 'gear noise is normal', I guess I'm out of luck from a warranty standpoint unless/until the box grenades.

Cmscaddyvwagon1

Hey Admiral B. I have the same problem. 2014 V Wagon made the noise with 12 miles leaving the dealer...

AdmiralB

I took my car to RPM Transmissions - they're ten minutes away - and they basically said it's normal. According to them, it's the dual-mass flywheel, and while mine is definitely at the noisier end of the range (victim of tolerance stack I guess), it's no big deal.

I also spoke with the service guys at the only Cad dealer in the area which I know moves a lot of CTS-Vs, and they said they've had the same complaints - "I bought a $70K car and it makes this noise?" - but "they all do".

I still can't believe they all make the noise to this degree. I can't find a single mention of it on Camaro forums, and there have to be a lot more M6 ZL1s being sold than CTS-Vs.

AdmiralB

Does your clutch pedal feel...weird?

Mine has a really short stroke (compared to my Corvettes and Camaro), and a little bit of 'dead space' before it meets significant resistance. Just kinda strange. It sort of feels like there's so much padding under the carpet, the pedal bottoms out against the floor before it completes the stroke.

Cmscaddyvwagon1

Hey Admiral B,
You are describing exactly what and when my car duplicates the dame noise. This said, I think is something in the exhaust and does not make the noise when allowing higher revs and some clutch slip- there is no lug with some slip. This tells me something is rattling during very low RPM's. Please let us know if you find anything out. I am trying with mine now, but the dealer sent me away stating that the engineers wanted more mileage as I still only have 200 miles on the car. You have 2000 and its still there, so I am not convinced this is something that will go away.

AdmiralB

I'm 99.5% sure it's not the exhaust. Mine's been replaced, and there's just nothing to rattle anyway.

I've had a camera under the car while making it do the noise, and there is no movement of the system. It'd have to move a LOT to contact anything.

And like I said above, I went under it while my son pulsed the gas in first, on stands - I couldn't get it to do the noise as prominently that way, but it's clearly coming from the flywheel area.

Exidous

iTrader: (11)

Sounds like it's time to bolt up a bad *** sounding aftermarket exhaust and keep the stocker in the garage for warranty repairs. It's always a shame when you hear stories like this about any such noise being "normal". If you drive a Porsche Carrera GT with that tiny multi-disk clutch sure you can expect from chatter but not on a Cadillac V.

I've never understood why the move to a dual mass flywheels aside from less work for the blocker rings due to reduced weight of the clutch disk(s).

AdmiralB

There aren't any systems for wagons - that I know of - besides Stainless Works', and it's way too loud for this application in my mind. Corsa has a muffler set; it sounds OK but $1100 is stupid for just a pair of turbo-style mufflers. Not to mention having to cut the factory setup.

I don't want MORE noise, I want LESS.

The applications where dual-mass wheels seem to make sense is engines with low cylinder count and very high (relative) torque at low RPM. IOW, four-cylinder diesels. You have fairly widely-spaced, large impulses, and the flywheel helps smooth them out.

Makes no sense for a V8 of any kind, to me.

Exidous

iTrader: (11)

Good points. I take for granted sometimes that I can fab up my own exhaust. I'd make something in dual 2.5" with a nice pair of magnaflows. Wouldn't be loud but would sound really nice.

AdmiralB

I really wish the NPP mufflers from the Camaro would fit. Actually, there is room but the inlet isn't quite in the right place. And the rear valence isn't set up to allow the dual side-by-side tips.

I like the exhaust note, really. It fits the car, IMO.

slowride

iTrader: (3)

Might be the dual mass flywheel making a little racket at low rpm idle.

Project GatTagO

iTrader: (7)

Older BMWs use dual mass flywheels, and I bet they don't rattle. Seems totally ridiculous that a brand new luxury car would make any sort of rattling noise. GMs excuse that this is a "performance car" is pure BS.

I would be livid and raise hell until it was fixed.

Andrew

Cmscaddyvwagon1

Admiral B, I have found resolution to the noise we both have in our manual V wagons. The dealer isolated the noise to the supercharger. They took the belt off of the supercharger pulley, test drove and the noise is gone, gone, gone. I was able to drive the car my self and can confirm this is it. Now, the car is sitting, with supercharger disconnected waiting on GM to get a fix for this. Apparently someone in the "V" design group is going to come up with something soon. I think the trouble is that this rattle is different then the superchargers that are being replaced for rattle at idle with no throttle input. Mine makes no such noise, but my 11 V wagon did. Hope this helps, let me know you got the message.

AdmiralB

It's not the supercharger. My noise is driveline related.

I may well *get* a rattling supercharger eventually, from my understanding, but so far that is quiet.

It's started making the noise - in a very subtle way, if I wasn't listening for it I'd probably miss it - on cold starts.

I'm pretty much convinced it's a resonance in the flywheel assembly, but nothing I can really do about that.