noise when idling

[GRunner]

um... this is not going away. before i take it into the dealership, i want to make sure I know what to tell the guy or to explain to him. seems like when the truck is idling, 2003 LX470, it will start making a "hummmmmmmmmmmmmmm" sound. like a constant low pitch sound. but it will go away if i take it off "D" or give it a little bit of gas. you think it is like an idling problem or something with the transmission?

thanks!

 

[Jim_Chow]

Does it sound like a plastic panel vibrating? Does it only do it when the engine is cold when it vibrates more?

I had/have a similar sound under similar conditions (when stopped at a traffic light w/ cold engine, usually cooler temps outside). The sound will sound like a vibrating body panel in the rear left quarter, but it's not. It wasn't until it occurred while parked at the grocery store w/ engine off (wife was waiting in the car), doors closed on a windy day that I figured out the source. Wife said she heard the exact same sound when a gusty crosswind hit. Turns out, there is a flimsy piece of plastic in the left rear wheel well that should be attached by the same bolts used to attach the mud flap to the body. When my kaymar rear bar was installed, the left side bolt holes didn't line up exactly correctly, so the installer omitted those bolts for that flimsy panel. Even after I reinstalled the bolts to bolt that panel directly to the body/bumper, it still occasionally will vibrate. The bolts really need to first go through the mud flap, then through the panel into the body/bumper since the mudflap changes the resonating frequency of the panel (this is by design). I can only do that by drilling new holes in the mudflap. To avoid that, I think the alternative fix would be to attach a rubberized aluminum like Dynamat to the back side of that platic panel to change the resonance frequency.

 

[Wellcraft19]

Or, said it before, I can be the ventilation fan that is vibrating. Speeding up will increase the voltage and noise might go away.

In any case, you have to do some trouble shooting to sort of exclude potential trouble sources. A/C on/off, fan low/high speed, voltage variations.

Try more and report back.

 

[richg]

I have a vibration when it is cold out as well. The big plastic engine cover vibrates against the engine when its cold and makes a stupid rattle sound. I've tried shifting the cover a bit on its mounts to no avail. Only happens when cold, truck in drive, but with your foot on the brake and sitting still (like at a traffic light).

rich

 

[NMuzj100]

richg - check the FAQ for Cat Shield rattle and see if it fits your symptoms.

Several other "noises" are addressed by TSBs so check the TSB threads too.

We can help more if you add vehicle data to your sigline.

 

[CrusrDug]

It was so windy here about a month ago I had a whistle coming from the front. I was in a good crosswind and doing about 80mph. Must have been catching something just right. I just figured my cruiser was happy.

Back to the Hmmmmmmmm. Have you turned everything off? Sounds like it's a lower RPM sound. Does it go away if your moving?

 

[richg]

richg - check the FAQ for Cat Shield rattle and see if it fits your symptoms.

Several other "noises" are addressed by TSBs so check the TSB threads too.

We can help more if you add vehicle data to your sigline.

Oh its definitely the plastic cover. I popped the hood one cold morning and watched it vibrate, then put my hand on it and it stopped.

rich

 

[CrusrDug]

What is the cover for? Strictly looks or is it protecting something? With all the heat this engine put's off, you think it would warp. Plus, containing the heat can't be good. I need to pop it off, I've never looked under it.

 

[GRunner]

CrusrDug, it "hummmmmmmmm" whenever it is stopped and it goes away as soon as I either gas up, or put the transmission in Neutral. If I don't accelerate and let it roll the noise is still there. So I think it is a low RPM sound.

 

[Jim_Chow]

CrusrDug, it "hummmmmmmmm" whenever it is stopped and it goes away as soon as I either gas up, or put the transmission in Neutral. If I don't accelerate and let it roll the noise is still there. So I think it is a low RPM sound.

Those are exactly the same conditions I'd hear the sound I had, but only when the engine is cold and when it's cold outside (50's or colder).