I am new here and this is my first post so please be tolerant of me.
I have a 2008 ES350 that I leased in Dec.
My engine makes a tapping noise (sounds like valve tap) when it first starts up. In the winter, the noise is much louder and lasts for at least about 5 minutes or more, depending on how cold it is outside. It is more pronounced when accelerating. Once the engine seems to be fully warmed up, the noise subsides. Now that it is summer, the noise is barely audible and only seems to last for a few minutes.
At my 1000 mile check up, I questioned the service rep about the noise and was told it was normal for this engine.
However, at my 5000 mile service, I complained again about it and described it as piston slap and the service rep was aware of it. He asked if I could leave the car overnite so they could listen to it after a cold start but unfortunately, due to circumstances irrelevant here, I could not leave the car overnight at that time. I will definitely keep complaining about this at each service interval, until either the noise goes away or I can determine whether or not it is harmful to the engine.
I have done some research on piston slap and while noone says it is good, I can't find definitive evidence that it is harmful, especially if it goes away once the engine heats up.
Although I shouldn't worry about this since I am leasing, I may likely want to buy the car at the end of the lease, but not if this issue isn't resolved. Right now I am sorry I didn't buy the 2005 ES330 I leased since that car had no quirks.
If piston slap is harmful, I think it would be unforgiveable for a car at this price level.