hey all, i have a 2002 highlander 4 cylinder fwd. i've just noticed this recently, but whenever the car is warmed up to operating temperature, there will be a strange ticking/rattling noise coming from the engine. you can't hear it from the cabin, you have to have the hood up in order to hear it. i'm fairly certain its not injector tick, as it rattles for around 6 second and then subsides for a little while only to come back for another 6 or so seconds. from the sound of things it sounds like its coming more towards the front of the engine, around the exhaust manifold area. i think it rattles in tandem with the cooling fans turning on as well, but i haven't tested this. any ideas? thank you!
lythrum
Some ideas:
Not unusual for the 2.4L to vibrate more when the AC compressor clutch engages and the idle drops a little. It may be vibrating at the right frequency to resonate a heat shield or exhaust coupling.
Are the cat heat shields tight, including the one on the back?
Use a mechanic's stethoscope to narrow down the location.
Might be an engine mount.
You could pull fuses on the AC compressor clutch and the fans to help narrow it down - but only for a few seconds.
You can tell when the AC compressor clutch engages - you will hear the relay click and the fans come on.
Not unusual for the 2.4L to vibrate more when the AC compressor clutch engages and the idle drops a little. It may be vibrating at the right frequency to resonate a heat shield or exhaust coupling.
Are the cat heat shields tight, including the one on the back?
Use a mechanic's stethoscope to narrow down the location.
Might be an engine mount.
You could pull fuses on the AC compressor clutch and the fans to help narrow it down - but only for a few seconds.
You can tell when the AC compressor clutch engages - you will hear the relay click and the fans come on.
CR made some great points, I remember seeing your exhaust clip and something was definitely rattling under there. As your car reaches operating temp, your exhaust flanges are going to heat up and expand. If your gaskets are worn or your mating surfaces aren’t in the best shape, you could very well get some metallic rattling, ticking or tin can noises as well from under there.
Shift the car between park, drive, & reverse and observe the changes in the sound, if any. Have someone do this while you are listening for any noises in the engine bay or underneath the car. While the car is running, spray down the manifold and all flanges with soapy water and see if you find any leaks as well. For my car, my donut gasket had to be replaced, and now I need new flanges for the two cats as they have lost a lot of material due to the rust.
Shift the car between park, drive, & reverse and observe the changes in the sound, if any. Have someone do this while you are listening for any noises in the engine bay or underneath the car. While the car is running, spray down the manifold and all flanges with soapy water and see if you find any leaks as well. For my car, my donut gasket had to be replaced, and now I need new flanges for the two cats as they have lost a lot of material due to the rust.
many thanks for the ideas, i will test your theories within the next few days and report my findings. already had a shop look at it and said they couldn't find anything.
I have found out the hard way that "getting a shop to look at it" includes you paying for them to pick their nose for 20 minutes and then them not being able to (or not caring about) finding anything.
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