Since the weather warmed up (last 2 months) I have noticed a noise coming from the right rear underside of the engine... Sounds like something in between "dakadakadaka" and "chufchufchufchufchuf".

 

car has 173k miles

 

What I know it's NOT:

 

spark plugs/wires/ changed them out.

exhaust leak/ patched 2 small holes between cat and muffler, tested exhaust system by covering tailpipe with a piece of cardboard pressed by hand... pressure built up in 3-4 seconds and caused idle to change.

 

other observations:

 

Intermittent P0325 code (engine knock sensor) Goes away after complete cooldown. Seems to only show up when car is driven multiple hours consecutively

 

The sound is timed with engine rpm not speed of vehicle, and is most apparent when accelerating, almost completely inaudible when car is not moving even when revved into 3-4 k rpm range.

 

Engine seems to deliver plenty of power/ no trouble merging into 70mph traffic

 

gas mileage is down maybe 5 %

 

Not burning oil, (no white or blue smoke) only adding 1/2 quart every 2-3k miles b/t changes

 

Head gasket is intact/ no mayo under oil cap or bubbles/oil in coolant

 

Exhaust manifold is solid/ no loose gaskets

 

All 4 injectors are ticking along normally

 

no major fluid leaks under chassis

 

Would adjusting the valves remedy this? 

 

any Ideas are welcome and appreciated. 

 

 

Suspect it could be bad u-joint on drive shaft going to rear wheels. My 99 OBW has started to make same muted sounds maybe like what you describe. My car noise sounds like ching ching ching. I can hear it even when backing slowly in reverse.

 

A bad knock sensor will cause you to loose 5 % in gas millage.