I'm trying to locate (still) this weird sound I get at about 2300-2500rpms if I only have a very light load while driving in 1,2 and 3rd. The noise is there only when I have a very very light load (for instance while maintaining speed at 2300 or if accelerating very slowly). If I press the gas it goes away, if I lift off it goes away. it's not there bellow 2300 ish, not there past 2500 ish. It's not loud by any means (the radio at a normal level will cover it completely).
I can't reproduce it on the driveway by just reving and holding the rpms to 2300-2500, which makes it even more difficult to figure out.

Now for the sound description: It sounds just like if you tap on a cast aluminum valve cover very lightly (but rapidly) with a socket (and yes I've tried it to see if it sounds alike and it's very close).
The "toc toc" sounds is quite fast, around 5-8 per sec at the noted rpm range (almost matching the valve train actuation if I had to guess).

I have checked the obvious: exhaust, shields, other possible loose items under the hood...nada
I've held rpms on the driveway from 700rpm to 2700 and nop, doesn't do it.
I've tried to see if it was the clutch, but again, can't reproduce while standing still, nor can I feel anything weird thru the clutch pedal either.
I was thinking a bad harmonic balancer but it appears to be fine and I don't see why it would do such a sound.
My next step will be to pope the valve covers, but base on my experience with alot more radical stuff than the vette, if it was valve train it would do it on the driveway and I'd hear it with the hood open.

Is there any other things that could "rattle"? I know with older cars, they had a PCV valve on the valve cover and sometime they would rattle and make a buzing sound (not at all similar to my sound though).

Car performs flawlessly in all aspects

 

it's a back up vacum pump you will also hear it at an idle tock,tock,tock very fast right?

 

I'm no expert and you should get a lot of good info here but if you're only experiencing it under load AND movement I'm thinking drivetrain. Since by your description it seems like the noise is coming from the front I'd say clutch is a good place to start.

BUT---that's just my guess and I'm not a mechanic.

Someone else will chime in with some good advice.

Best of luck with it.

 

nop, at idle, it's not there...it's only there during that very particular driving condition (very light load/maintaining rpms while moving forward) and at that particular rpm range.

 

yes I was thinking maybe some clutch chatter, which would get amplified due to engine harmonics at that rpm range...but...pulling the clutch is a total mother, so unless my car doesn't want to move, fat chance I'm spending 8h on my back .
Plus, it's not loud and you really have to know to hear it and have the radio off.
I have had weird stuff happen on engines before, one was a solid roller lifter comiting suicide and re-crinding the cam...it had this random "ting" but, it made it at idle so it was easy to figure out it was internal...
this got me completely clueless!

 

I had the same sound about 6 months or so ago, it went away but I know what sound you are talking about. It sounded like it was coming from the valvetrain. Weird.....

 

ah HA! so I'm not alone out there!

 

this AM, driving to work, after the car warmed up (so towards the end of my commute) the noise was almost completely gone...I really can't put my finger on this...

 

I hear it then too, anytime the vacume pressure's to low