Details: '07 PreRunner double cab automatic V6, purchased with 120K a few months ago, I haven't done any mods and I don't believe any were done by previous owners
Problem: From a dead stop, there is a chirping noise from under the truck as it accelerates. The noise is not coming from a belt or bearing in the engine bay. It is not the type of constant squeal that you have with a bad water pump bearing, fan bearing or belt but more akin to the rhythmic click of a bad valve. It is most definitely cylindrical in nature and is directly related to tire RPM. A slow acceleration means a slow chirp and the frequency of the "chirping" increases as the truck accelerates. If I let off the power, the sound goes away and will resume at same frequency when I get back on the gas. Shifting is normal and does not affect the noise at all. It only occurs under power and will diminish as speed increases and will eventually cease around 35-40 MPH. Does not occur in reverse and does not happen in neutral when I rev the engine. I have greased the u joints on the drive shaft (stock, 2 piece) and the hanger bearing with no improvement.
Any suggestions would be greatly appreciated. Thanks-