I bought a 2000 tacoma 3.4 last year. It currently has 152k on it. The timing belt was replaced at 99k along with the clutch and water pump. I had all the fluids replace and running amsoil. I replaced all plugs and wires, had injectors cleaned. K&N air filter. Lately (past few months and getting worse) I have been hearing a knocking when accelerating, under load, and at low rpms. Usually doesn't happen in first gear and it doesn't happen when the engine is cold. If I let off the gas and then accelerate again, it sometimes goes away. I am running 87 after mech told me not to run premium. Not getting any check engine or loss of power. Sometimes I think I can feel a little hesitation when accelerating at high rpms.