I've noticed a rattling noise coming from the engine, when taking off from a stop or after slowing down almost to a stop. It sounds like valves when you are in to high of a gear, while trying to get going.
It used to happen very rarely, but now it seems like it's happening more often.
I use 91 octane fuel and get oil changed regularly at the dealer, using dino oil and at factory intervals.
Any ideas? should I be concerned?

 

How hard do you run the car?

 

Perhaps try to record the noise for a better opinion/response. Regardless I hope it's nothing major and you're able to get to the bottom of it.

 

Buy an engine stethoscope from Harbor Freight have your buddy rev it in park and move the sound tube around until you know what area the rattle is coming from and report back.If it's normal in park even with rpm increase,then it's probably something drive line related.

 

I have the rattle too, mine turned out to be the cat's heat shields. I finally got tired of hearing it and just stuffed some steel wool to quiet it down.

 

"Engine rattle" is far too vague for an internet diagnosis. Please give more details so that we can figure out what it is and give advice.

 

It would be very hard to catch it while driving, it's not consistent. You can't replicate it while parked. Most of the time it happens when I come to a stop, slow down to a slow roll, and take off again. It will only do it at the initial take off, and only for 1-2 seconds, and only while accelerating lightly, not hard.
It only happens for 1-2 seconds and than goes away.
I don't beat on the car, I do drive it hard here and there, I go WOT maybe once a week.
It sounds exactly like when lifter chatter...

 

What octane gas do you buy? Since OHC engines don't have lifters, this sounds suspiciously like detonation.

 

Overhead cam engines do have lifters they are commonly called shim over bucket some even have rocker arms, as far as acting goes I would imagine you could run 87 and the knock sensor built-in to the computer would retard timing so that you wouldn't have any detonation

 

Octane not acting

 

Perhaps you are thinking of push rods

 

As far as the engine not making noise when you are parked and running it but it will when you're moving under a load that is very Driveline oriented sounding to me. I will mention this also sway bar end links make a clunk noise when you're going very slowly I had to replace mine they were all shot at 73000. Anything that would make noise within the engine while under load would probably also make a noise while Park and revving even if it were some sort of a pulley bearing like water pump or alternator or AC or power steering pulley

 

u talking about the weird "wind-up toy" sound you can hear when ur coasting and off the accelarator and driving next to a wall on the side? if so or if anyone knows wat im talking about wtf is that sound? those who drive in parking structures should know wat sound im talking about.

 

OHC can use a bucket between the cam lobe and the valve tip. Some engines have shims on top of the bucket, others have them underneath. I haven't looked at a VQ top-end but assume it's like my SR20 with hydraulic lash adjusters (HLAs) with rocker arms with the cam lobe riding on a pad at the mid-span of the rocker.

I'm old, so a lifter is something found in a cam-in-block engine riding on the cam lobe and actuating a push rod which pushes the rocker arm to actuate the valve. I had one of those lifters collapse due to varnish on the Oldsmobile small-block powering my 1972 Cutlass.

The 1600 in the Datsun Roadster used solid tappets (lifters) and adjustment was a lock screw on the valve tip of the rocker arm. I could never get that thing to run quietly.

I haven't heard noisy HLAs; don't know if that's fundamental or I just never came across an old engine with noisy ones.

 

Yeah if you have a bad hydraulic lifter it'll make noise