You may want to stay out of boost and get the tune checked. It could very well be detonation in that certain RPM range.

Prolonged detonation will put a hurting on the rod bearings and they'll eventually give out.

Running on GTM's base tune. I sent in logs several months ago and never got a response.

I had the car on the dyno a couple of times and the AFRs are good. It is pretty rich. Plus this noose only happens when I let off the throttle abruptly from at least half throttle in higher gear. It doesn't do it otherwise.

This was a common problem on the 350z's ,it happend to me on my 350z so far so good on my 370z.

Ahh, base tune is all you had to say :)

I hope you get it figured out.

Jus to be completely safe if I were you I'd get a custom tune so that it can be on the money. No need to run extra rich when a tuner can dial it in n make it run smoother.

Sam's tunes are normally spot on at wide open throttle with the air / fuel numbers. 450whp is conservative, but not all gas is created equal. Running too much timing on a canned tune could turn fatal if the tuner isn't able to watch all that is going on.

Where are your numbers around? 11.1 - 11.5 a/f at wide open?

At wot I'm around 11.2.
Still regardless a generic tune doesnt compare to custom. Altitude, gas, humidity, weather in ur particular state/city you live in plays a factor. When I mean by custom tune u should look for a reputable shop close to you not jus anybody. In the end was worth it for me. I was running really rich but I'm sure Sam does that for the extra safety, but again there was no need to run that rich (well me personally).
At least get it on a dyno n have a competent tuner check it all out.

For sure man

Yea, the AFRs are in the low 11s to redline. If you look at my dyno charts, there's no oddities. Curve is smooth. One of my friends test drove it yesterday since it was nice can "cold" out (no worries about power drop). It runs great all the way to ~8-9 PSI. TCS keeps kicking in even in 4th! Haha. Once he felt comfortable, he turned it off and handled the car as it got squirrelly under boost. He says it felt scary, but it was quite fun. This is coming from a Lotus owner :)

Right now I'm still on the fence: Continue with cooling and exhaust upgrades to the final tune of about 500 whp or sell and build up an NSX (depends on job situation as well). I'm pretty sure the new throttle map and VVEL tune will spice things up and make the car even more fun to drive and make me forget about wanting an NSX.

Ah... here's the post from another forum (hopefully not blocked)
MyG37 - View Single Post - klonking noise on start up.

See if you can download this MP3 file. This is the same noise I hear on engine start. Unfortunately, this is something I heard every so often before the turbos were installed. At the time I could not find any answers whether this was a serious engine issue or not.

This is a similar noise when abruptly taking foot off the throttle given a decent amount of load in the higher gears like 6th. This is something I've not done lately because I was testing for slippage in 6th at 40 MPH.

I've looked up other videos about rod knocking, and it is a similar sound. Yet, my car runs and sounds fine at with normal or hard driving (other than the test mentioned above). The noise isn't there at idle (very frightening when watching some of the videos on YouTube).

OMG, from G37 Forum someone posted a thread here from Daishi! Haha...
http://www.the370z.com/engine-drivet...k-startup.html

Manual? Might be a your throwout bearing. One of the arms could have bent perhaps, or even broken off. I did that with my 97 Type R Integra...several times. Similar 'clanking' until I did a clutch/flywheel replacement and saw the bearing shot to hell. The bearing housing was in the place it should be, but not seated because of the broken arm and would rattle upon acceleration and engine braking.

Put the car in neutral, then slowly rev it all the way up. Then come down slow on the accelerator. Is the noise present?
Still in neutral, rev up quick, hold for 5 secs, then come off it fast. Any noise?
If yes, you might have a serious issue. If no, start looking under the carriage for rocks between rotor guards, worn cv's, then you might have to open the transmission and look at the bearing.

The honda trans had a bearing with two 'hook' arms. One broke off, and the noise was the only indication; no difficulty shifting, no 'grinding noise' etc.

Best of luck!

Thanks for the suggestion. There's a dust cover under the transmission so one can peek at the CSC bearing. It's fine for normal or aggressive driving other than abruptly taking foot off the gas under heavy load at low speeds. I honestly haven't performed the 6th gear clutch slip test for the past several months since getting a new transmission (prior, new clutch disk).

One more for thought...

Check your trany and differential mounts. One may be split and allowing those parts to knock against the frame.

Thanks. I'm going to get those inspected very soon. Lately the car shakes from juddering whenever I go in reverse. I have to feather carefully or the car shakes violently. It happened before when the car was new, and it started happening again even with an aftermarket clutch. It comes and goes.

Bringing this thread back... I'm hearing this fast "clacking" noise every once in awhile in 1st at low RPM as I get the car moving. It's just casual acceleration. It sounds like a machine gun "clack-clack-clack" sound, and it's brief. The car doesn't judder, so it's smooth.

Earlier I wrote that this sound can be heard if I briefly hold the throttle down in 6th at low speed around 40 MPH, and quickly lift the throttle. It's the same sound, but now I'm intermittently hearing it in 1st at low speed.