Loud rattling - source?

[goldNSX]

My Lysholm CTSC has 25k miles on it and something makes me wonder where the noise is coming from. Scenario: when I park the car for a short break (5 minutes) on a hot day there is a loud rattling around 3500 rpm at partial throttle after the restart. It goes away under WOT and off the throttle and also goes away on the first mile after the break. I've the OEM engine cover installed, so I guess that it's related to heat in the blower. The blower unit gets hot during the break. It doesn't sound like a rod-knock or engine bearing failure. Any ideas?

 

[jwmelvin]

Any chance you can take a video to record the sound? I know it can be hard to hear in a recording but it's worth a shot.

 

[goldNSX]

I'll try but it's very hard to do.

I had i several times today esp. after the car was sitting for a short pause. With the car not rolling there is no rattling at around 3500 rpm. After taking off with a light throttle it's there. MY first guess are the driveshafts as the car has now 110k miles. But I don't have an idea of them going bad on an NSX what they sound like.

 

[goldNSX]

A little update: I've checked the axles: they are ok but the gearbox seem to be quite noisy (marbles like). Now the noise is present while the car still stands after a short break. The difference: with the clutch pedal pressed/down NO rattling. But with the clutch pedal up something rattles at 3500 rpm. So my guess is that it's related to the TOB or another bearing in the gearbox. How common are ISB (input shaft bearing) failures in the NSX? I know that other Hondas often have this problem. I'm at 110k miles now.

 

[goldNSX]

Update: When I press the clutch pedal lightly the rattling goes away while driving. So I guess it's not related to the CTSC but to the TOB or gearbox. Clutch is overdue anyway.

 

[foundry3]

Update: When I press the clutch pedal lightly the rattling goes away while driving. So I guess it's not related to the CTSC but to the TOB or gearbox. Clutch is overdue anyway.

What clutch is it?

 

[goldNSX]

Still OEM. The disks have been replaced at 40k miles with OEM. 110k on the car now. Problem still there.

Comparision to a friends car: it's definitely a problem in my gearbox, most likely the mainshaft bearings. Planning a full revision of tranny and clutch next winter season.