I?ve heard several four-cylinder Toyota Tacoma engines with an annoying ?clack-clack-clack-clack-clack? noise at low idle – particularly my 2004 with 49K miles. A sound almost like a noisy valve but isn?t. It sounds more, shall we say, robust. It seems to come from a lower part of the engine. Toyota service people tell me these engines all do it.
Can anyone tell me what it is?