Hey guys. Recently I have been noticing a engine rattling sound under heavy acceleration only. It only happens for a few seconds and then is gone? I cannot narrow it down, I have been under the car and nothing seems loose.
Has any of you experienced this and what was the conclusion when you figured out the problem?

It's hard to explain the sound it's just a Metal rattle coming from the engine bay lol? I dunno any suggestions?

 

I had the same problem when I had my Cayenne V6, in my case it was about injectors, I started using premium fuel and a few bottles of injectors cleaners and bam the noise was gone. I never had any rattling with my XJ though, and it has 83k miles on it

 

Injectors making the sound huh? I dunno sounds a little weird to me. Anybody else have an opinion?

 

Like marbles in a coffee can?

 

Sounds like classic knocking. Are you using premium gasoline?

 

Marbles in coffee, you could say that. I only use shell premium on every fill. I just put in a whole can of sea foam into the gas tank which is 1/4 full. Going to run it almost out and go fill her up.

 

My only suggestions would be bad gas, snout of a supercharger's bearing going (which I don't think you have an R) or spark knock. The timing on these cars have alot of factors and outside of my knowledge. Maybe a tech on here can shead some light.

 

Does it only make the noise under load, or will it do it in Park or Neutral as well? If it does in while the vehicle is stationary have someone give it some throttle and you might be able to pinpoint the location of the rattle a little better. Something I always do is have someone ride with me when I replicate the scenario. A second set of ears does wonders.

I dont think it would be coming from the valvetrain, because the rattle/knock is usually pretty consistent at all RPMs, and usually more noticeable at idle.

 

It does not do the sound when I rev it up in park or neutral it only does it indoor heavy acceleration. I cant figure it out lol.

 

Mine knocks a little under heavy acceleration for about 3 seconds then goes away; it sounds a little like something is rattling. It's done it religiously since I bought the car. The dealer said the car is fine and the engine management system will adjust quickly while accelerating to stop whatever causes the sound. I've had the fuel injector service done by the dealer (at their recommendation) and that didn't change anything. Clearly I'm not a mechanic, and my explanation isn't very detailed (in the technical sense) however my issue sounds a bit like yours. It doesn't do it when siting still and revving the engine - only when I get on the throttle.

 

Still sounds like knocking to me. Try a different brand of gas and see if it still happens.