Brief chatter noise between 2500-3250RPM?

[svenfendersen]

Hi, folks-

My first post here! I have a 2013 FR-S 6MT, with ~15k miles. I adore it. However, I am hearing an odd engine noise, typically when I rev match on a downshift and the engine revs from ~2500 to 3250 RPM, and the noise seems to occur right as the engine revs past 2800 RPM. It's a metallic chatter/rattle/lashing sound that happens for a fraction of a second as I go from off throttle to a quick on-throttle blip (with clutch engaged, so motor is 'unloaded' for a rev match), but sometimes I hear it in gear under load if I alternate off-throttle to half-throttle (or more) around 2800 RPM. It sounds pretty much just like my old M3 did when it had the dreaded VANOS issues, but a little less dramatic. Here are a few other factors:
1) Does not happen every time I drive it, but I hear it once every few days
2) Only occurs when the car is warm (more than 5 mins of driving)
3) No CEL/codes or anything
4) Engine does not stumble or surge when the noise is made. No appreciable loss of power when I hear it when the car is in gear.
5) Car is totally stock except for a Perrin cat back exhaust.
6) I run Shell gas, 92 octane (highest octane I can seem to find in the seattle area, sadly)

I've been looking for a thread about it on here and the closest issues I seem to come across are folks that have more sustained rattle sounds when completely off throttle slowing to a stop.

To me it kind of sounds like a timing chain could be slapping against it's cover, or the chain guides, as a result of sudden tension as I go from off-throttle to on-throttle. Maybe a loose tensioner? I was thinking maybe it could also be a loose heat shield, but I haven't had a chance to investigate that much. I figure I'll have the dealer check it out, but wanted to see if anybody on here has heard similar sounds. Any insights on this would be awesome... thanks!

[strat61caster]

I get noises like you describe when free revving the motor in between shifts, especially when the clutch just starts to contact as my foot is coming off the floor or when I stab the pedal to rev it up. Two things going on there for me:

1. A rattle/grinding/buzzing between the engine and transmission as I'm overlapping my pedal inputs, basically eliminated as I became more deliberate and figured out how to shift smoothly with this car.
2. The throttle body is by wire and makes an alarming noise when it snaps open, see this post:
http://www.ft86club.com/forums/showp...20&postcount=3

If neither of those sound right then go to the dealership, it sounds very reproduce-able by your description. Good luck

Edit: I forget about the VVT noise that Dezoris posts about below, that's probably what you're hearing.

[Dezoris]

Its probably the VVT rasp/rattle noise that is present during quick cam advance.

Please listen at about 3:13. At 3:15 you will hear the sound which I think you are referring too. [ame]http://youtu.be/wGcv6SKj858?t=3m14s[/ame]

Can you confirm before we get into anymore discussion?

[svenfendersen]

Thanks for the prompt replies, Dezoris and strat61caster!

Even with headphones on it's hard for me to make out what noise I am hearing in the Vortech FR-S Track Testing video at 3:15, but I'm assuming it's the same thing as in this under-hood clip you guys pointed me to, which sounds about right: [ame="https://www.youtube.com/watch?v=g8nnFeP7ib0"]Frs/Subaru Brz "tip in knock"? and VVT sound - YouTube[/ame]

I havent mic'd my car under the hood to record the noise, but even from the driver's seat it sounds similar enough that I'm pretty sure that's it. Glad to hear I'm not the only one encountering the sound... owning an E36 really got me paranoid about expensive valvetrain failures!