I need help diagnosing an intermittent engine noise heard only at idle. Seems to be coming from the driver's side. From a cold start (27F) the noise isn't there. After running idle for 12 min in my driveway, I started recording this clip. It starts quietly at 20 seconds in. Then at 0:55 it goes double time until it stops suddenly at 1:44. It starts again at 2:02, and speeds up again at 2:36.

http://drive.google.com/file/d/1PDqU...ip&ts=5c4cafc3

The car is a 2001 UL with 129K miles.

 

That sounds like a loose spark plug and the exhaust is coming out of the spark plug tube! However, I can't explain why it changes from a regular helicopter noise to a very fast helicopter noise!?

I would CAREFULLY pull off those coil packs on the driver's side, and wrench down on all 4 plugs to ensure all they're tight. Crazy sound, but swear it sounds like it's coming from the spark plug tube. U can also take a tube of PVC or even a skinny broom handle to act as a stethoscope and probe/touch things to find exactly where the noise is coming from.

 

That is s strange noise!

I'd say do the above first, may get lucky, but I'd get that valve cover off asap and inspect the cams/lifters/valve springs

 

It sounds like a fuel pressure regulator in an unhealthy state. I noticed the temp on your dash reads 27 degrees. A little water inside the fuel system below freezing can cause fluctuations in fuel delivery. The pressure regulator, there are 2 both are in the back just above the rear spark plug coil pack, maintains the pressure of the fuel rail. When the regulator can't do it's job it creates oscillations in pressure which will make noise.
Lexus calls it a "Fuel Pressure Pulsation Damper"

 

I have no idea, but when was the last time you check your fluids? I am wondering if it is low in engine oil?

 

 

Thanks for the suggestions! The sound seems to be loudest when the camera/mic is directly above #3 cylinder. I'll start with checking that spark plug, then I'll replace the coil, followed by the fuel pressure dampers. Didn't see many posts about fuel injectors going bad on these engines, but I might try that if nothing else works. Its such an odd sound being that it is intermittent and changes speed independently of engine rpm.

The 2001's are 18 years old now, but I just paid the ransom for new engine mounts on this one so I plan on keeping it for a long time.

 

If it's still a mystery I'd buy a cheap ($10 or less) stethoscope from AutoZone or Harbor Freight. Even an ink pen will transmit vibration you can feel consistent with the clicking.
No sense throwing parts at the problem until you've narrowed it down somewhat. I would also check the valve cover bolts as they are prone to loosening over time. Don't be surprised if they are not even finger tight. The torque spec is very low, 53 inch lbs, so use 1/4" a drive ratchet to avoid over tightening.

 

Turned out to be a broken fuel vapor feed pipe, part #23818-46110. I'm surprised this didn't trigger a DTC light

 

Glad it was an easy fix!