I got this weird sound emanating from the engine bay, its very metallic and makes a rattling sound. Usually occurs when the vehicle pulls away from a stop and the engine is under a lot of load. (Trying to pass on the freeway or going up a long steep hill)
I only hear it above 4500 RPM.
Its not very loud and I don’t notice any issues with my MPG or overall performance.

Time for a valve adjustment? Or may it be something else.

 

Did this start suddenly? I'd suspect knocking from low octane gas from your description. I'd also expect it to throw codes (check engine light) if it got bad enough to hear it. Try higher octane (although this shouldn't be necessary, it will at least rule this out).

Probably valve lash. Get a mechanic to listen to it. The two noises are very different.

How many miles?

 

Any video of the sound?

 

4500 rpm is about when the VTEC starts to kick in. What year is your car?

 

Sounds like EGR knock. http://www.swri.org/3pubs/ttoday/Sum...n-and-Cool.pdf

 

I'd take it to a mechanic. Engine knock is not normal and potentially damaging. Could be an egr malfunction. I think the engine's knock detectors would go nuts trying to compensate. Maybe they are (but I would have expected a check-engine-light and associated codes).

If it's valve lash, then it's not so critical, but things like MPG may suffer.

 

Thanks for all the quick feedback and input, I tried to get some audio clips with my Go Pro but the sound is very subtle and hard to pick up, Like I said before I don’t notice any issues with my MPG or performance. When I have to fill up again I will try midgrade as see how that goes. I suspect the gas I’m getting is poor quality, you would think with the price we pay it would be better… but that’s being optimistic haha.

2010 Sport
40k Miles
K&N Intake and Cat Back Exhaust

 

I think you're on the right track for diagnostics. You could have enough carbon build-up to increase your compression where the cheap gas ignites too early under heavy load. It's an inexpensive first try. Let us know how this works out.

 

why go halfway with midgrade? If you want to cross off that possibility definitively, Just get 1 tank of premium to really see if it helps and you won't be left with questions if that was the cause. If it fixes it, then maybe you can backdown to midgrade or regular as your 2nd test.

 

What if it does fix the problem, is it just covering up the "real" issue by using better gas? the last thing i want to do is use more expensive gas... kind of defeats the whole concept of having a fit in the first place.

 

Well, I'm no mechanic or even vaguely an expert..

But if it does fix it,wouldn't that narrow down your potential issues? Something like carbon build up from poor quality gas (if so, wouldn't matter what car you were using). Narrowing down the issues can lead you to a solution...getting the engine c"cleaned out" or tuned up, etc.

Doesn't mean you're forced to run premium gas. If nothing else, maybe it means you should find a better quality gas station.

 

I don't think it will cover up the issue. It can be used as a diagnostic tool. Maybe the situation can be remedied with a little more knowledge. If it's carbon buildup, it's possible to clean the cylinders, for example. If there is another cause, there might be another fix, instead.

 

What Goobers, Ray, and Albert said.

If higher octane fuel fixes the problem, then you know it's engine knock (detonation) and not valve train noise. You shouldn't have either. You can always switch back to regular gas. If you think you got bad gas, probably be a good idea to switch retailers.

If the noise comes back on regular gas from another station, best have the thing diagnosed by a pro.

If it's valve lash making the noise, they need adjusting. You should hear this at idle under no load though. This is not a warranty item.

If it's something else, it should be covered by warranty. Keep in mind the power train warranty is 60K/5 years. Warranty service might require returning the intake and maybe the exhaust to stock.

 

if you watch more episodes of House, you will see the logic of if you were planning on a test of using midgrade, you might as well go all the way and go to premium for your test.

You want a definitive test to knock multiple possibilities out in 1 go and possibly save the patient as soon as possible before the hour show is up.

When you get a Result (in the british sense, meaning a positive change) Then you can back off and fine tune your subsequent tests to find exactly what you need to do.

 

Its sounding more like gasoline phase separation. Higher octane will help. Will need a fuel dryer too like Iso Heet and use half a bottle to a full tank.