Here's the problem. One day after taking my 08 automatic to the dealership for the complimentary oil change (4000 miles), I started hearing a noise from under my hood. The best way I can describe it is a muffled helicopter type sound. It only does this when my rpm level reaches about 500. When I come to a stop in raffic or at a light the noice creeps up to a continuous knock and persists until I let off the brake. Just letting off for a second to allow the rpms to rise causes the noise to quit. When I get back on the brake, it creeps back up. If I put the car in neutral, the rpms go a hundred or two and the noise quits. If by chance the noise is just on the cusp of starting, I can press up on the window switch with the windows already rolled up and the rpms will drop slightly and the noise will begin. I took it to the dealership and they checked the oil pan shield and looked the car over. They took it for a ride and said they didn't hear anything abnormal. Also hooked it up to diagnostics. Took it home, more of the same. Took it back Said they were able to replicate only once when the cooling fans kicked on. On my invoice, "When cooling fans come on idle does slow some" Also said that they never heard anything abnormal again. I was pressed for time so I left again.
I'm off this Thursday. anyone have some feedback as to what this could be. I'm making sure the service tech rides with ME this time. It makes the noise about 80% of the time that I come to a complete stop and the car is in drive. Could there be an alternator problem? I am pretty clueless about mechanical problems. Definately a very noticeable noise. Oil was 5-20.
Thanks.

 

its youre hood rattling. open it up and the rubber things 90 degrees and it will be gone

 

If it is the hood rattling, here's miketf1's solution explained more clearly:

There are two big black rubber bump stops on the front left and front right side when you open the hood. Just turn them counter-clockwise a half turn; if that doesn't stop the rattling, turn them another half turn... you're done, now close the hood and go for a drive!

 

i have this problem too...thx for the fix

 

thanks cionide.. i re-read my post and it does seem very vague..

hope this helps corsair!