That could be almost anything. Your best bet is probably a trip to the dealership to have them check it out.

 

whst else could it be? no change in performance, no vibration at idle or in motion at any speed and the sound comes and goes

 

its normal, it makes that noise for almost all of us.

 

I haven't noticed anything like that. I'll have to give it a close listen when I get the car back from the service department.

 

So my car isn't the only one, eh? Soft, faint rattle that cycles sinusoidally at about 1.5 seconds between sounds? Only at idle when warm? Mine has been doing the same thing since it had about the same miles on it as your car does (I now have 144,000kms or 89k miles).

This is NOT the sound caused by a bad water pump. I had to replace mine at around 110,000kms and it was a more constant metallic howl/chatter that sounded a bit like a supercharger further up the RPMs. It also puked a bit of coolant at the pump and the pulley/belt threw some coolant up onto the inside of the hood. See this thread re:water pump, includes the TSB:
http://www.toyotanation.com/forum/149-10th-generation-2009/381950-faint-noise-engine-compartment.html

It's been suggested to me by several mechanics that the noise could be caused by componentry of the variable valve timing system. The noise seems to be coming from the top-firewall side of the head, so that seems like a viable idea. It was recommended that I hook up a code reader with live data capability and watch the cam angle to see if it modulates in time with the sound.

There is a TSB regarding startup noise which involves cam sprocket replacement, but I'm not sure if that would be the culprit for this constant warm idle noise.

 

mine was making a grinding noise on cold startup,the tbs was for the timing gear .since replaced has been fine

 

My car just started making the noise you described. Was curious if you got it fixed? What did the issue end up being and what was the cost to get it repaired?

 

I have the same noise, i wonder if you found it? thanks

 

Well I have replaced alternator and water pump and those noises are more constant. When I had the noise I believe that you speak of it was the timing chain tensioner. A 40$ part that is located on the back side of the motor just above the oil sending unit. Quieted the motor down and returned performance that I thought was lost to other wear and rear. Also helped a hard downshift issue that I had for over 100,000 mi. Car currently has 245,000 mi. On it and runs great! On second alternator at 140k mi. third water pump every 120k mi. Second timing chain tensioner 220k mi. Second blower motor 140kmi. Second blower motor resistor 244k mi.

 

What year is your corolla? I hear this kinda tapping or ticking noise on low rpm throttle but not on idle. could this be the timing tensioner? it does on a cold or warm engine.

 

I would first look at your heat shield near the gas tank. Maybe it's loose and vibrating on the exhaust. Mine is loose on my 06 corolla. One of my plastic tabs next to the side skirt broke back in 16. I have zip tied it.

 

I have checked that twice, nothing is loose or making a noise!

 

The OP described it as a grr grr sound, only noticeable at idle. Mine has done this since new and is the a/c compressor cycling. For this one, try turning off the a/c (and defrost, and recirc since those may turn on the a/c without any other indication). Very predictably, when I do this, the grr grr cycling ceases. I could describe the sound as somewhat like a hydraulic power steering pump, except we don't have one.

This thread has other noises described, which are caused by other problems.

 

Yes, when i turn the ac on, the sound goes away gradually. It seems to be the compressor cycling.
Is that something concerning?
A mechanic said it's the alternator that does not charge enough, my car's noise is not only that one, i feel like there is another cause too. It goes up when i push gas pedal, that is why.