I am having scratching noise on cold start up and it only lasts a few seconds then it goes away and while accelerating, if i stop accelerating (leave my foot off the gas pedal) the scratching goes away, when I slightly accelerate the noise comes back again, if I stop the car the noise is not present, I checked all my engine pulleys and installed a new serpentine belt, this noise is killing me, if anyone has any idea please help me guys, thanks!!

 

are you sure your crank pulley (harmonic balancer) is fine? i suspect it's coming apart at the rubber and rubbing against the timing covers.

more:
https://www.clublexus.com/forums/ls-...-failures.html

not for an LS400 but you get the idea. yours might be completely splitting!

 

Don't you use an oil filter which has a poor anti drain valve?
Some aftermarket oil filters use cheap material for the anti drain valve and it leaks the oil and it can't hold the oil in the filter well enough. As the result, the oil pump needs to fill the oil to inside of the oil filter. While filing the oil at the start up, the engine runs without the oil and this makes some mechanical noise due to the lack of the oil pressure. I worry that you are having this problem. For the confirmation, I'd try changing the oil filter selecting a good Lexus/Toyota branded one.

 

I haven't checked the crank pulley, I will take it apart and check as it's the only pulley that doesn't move while the serpentine belt is off, thanks brother, I was suspecting that it could be my heat shield.

 

Thank you dear! This is alarming, I haven't really thought about that, I will make sure to use a genuine oil filter and give it a go!

 

Hello guys, the sound am talking about is exactly like the one in the link below, however in my case it's not the heat shield as I have checked that, anyone has an idea? Just please check out the video that has this sound I randomly found it on YouTube.