... coming from near the front of the motor. It's difficult to describe; it kinda sounds like a preignition 'knock' or maybe muffled popcorn popping ('been 'round small blocks for 30 years - never heard this). I only hear it at idle. With the hood up, it seems to becoming from the front - perhaps the water pump is going? But no leakage or weepage. No trouble codes on the scanner. Runs great ... so far. I'm inclined to rig a stethoscope of sorts to determine more precisely where the noise is coming from.

Any advice would be greatly appreciated.

'98 f150 4.6L auto, ac, all stock, 95K miles (92K on syn oil)

Thanks in advance

 

Is it kind of erratic, ie: not following the engine rpms? I have had this noise since about 75k. At 115k now, and it hasn't died yet. Might be the chain drive for the cam, that's the best theory I could come up with anyway.,,,,98

 

It might be your lash adjusters. Mine went out at 75k so I replaced them, no more noise. The internal springs on the adjusters had totaly given out so with low oil pressure they would rattle...once oil went through them, they shut up. hope this helped.