MY 6L V8 makes a loud knocking noise only when it first starts for only about 30 seconds then you never hear any more knocking for the rest of the day Is this a valve problem?

try going up a grade in viscosity ( from 15 w to 30 w)
ensure that only quality filter is used with an anti drain back valve in the filter El cheapo units miss this valve
possible worn hydraulic followers are allowing oil to drain back when stopped and it takes a few seconds to build up oil pressure

It sounds like one of your CV (constant-velocity) joints is going bad. This is common on front wheel drive vehicles. The CV joint allows the drive axle to pivot as you turn the wheels. Over time the protective boots crack, the grease leaks out and you end up with the knocking noise you describe when turning while accelerating. The dealership should easily be able to inspect the CV joint boot and diagnose the CV joint.

check the valve adjust and see if one valve is lower/higher than the rest. The valves are hydraulically adjusted and if the knock is really loud watch for a slight miss at rpm's. The only thing that will give a loud noise is a loose valve seat insert. You may pick it up with a compression test.

Go with a completely damaged & blocked exhaust converter

Air In --Air Out Yours doesn't go out & the trans gets confused
& can't use the shift strategy it was born with

That is the 30 mph or a gas filter really clogged,not real likely

What is with the noises?

Turning & just sitting still?

What was the trans shop diagnoses,was it test driven
& did you go alone,have to do that

Your car --so your part of the solution,be proactive

We had the same issue on our 2009 Flex. The problem was the motor or the gate (I can't remember which) that switches where the air comes out for the climate control. Took it to the dealer and had it replaced under warranty. It didn't take long (maybe 30min - 1hr).

It seemed like the system had a built-in fail safe that shut the motor down after a few seconds when the gate didn't make it to the desired selection. If you change the blower around when the fan is running (e.g. switch from floor to bi to dash to defrost), you'll probably hear the thumping come back as the gate tries to move, but can't.

HELLO; IF THIS NOISE IS COMING FROM THE DRIVER SIDE FRONT WHAT YOU ARE HEARING IS THE ELECTRIC AIR PUMP WHICH IS NORMAL UNLESS IT IS REALLY LOUD OR MAKING A GRINDING NOISE. tHIS PUMP IS PART OF THE EMISSION SYSTEM.

Smoke on start? Could be a valve problem where all your oil is in the bottom at start? Belts are squeaking too? Maybe a tensioner went bad?

Saw this service bulletin---

TAPPING / KNOCKING NOISE FROM ENGINE AT COLD START
This bulletin amends ITB02-049. This version amends the Applied Vehicles.
Please discard all paper copies of the earlier version.
APPLIED VEHICLE: 2002 - 2004 Q45 (F50)
2003 - 2004 M45 (Y34)
2003 - 2004 FX45 (S50) with V8 engine.
IF YOU CONFIRM:
A tapping or knocking noise (similar to a piston or valvetrain noise) when starting a cold engine,
NOTE: The engine is considered “cold” when it has been OFF (not running) for several hours.
ACTIONS:
1. Dislodge and remove any carbon deposits that may have caused the noise and confirm that carbon
deposits were the cause of the noise.
• While the noise is occurring, quickly rev the engine several times to approximately 4,000 RPM. Then
release the accelerator quickly, as soon as the engine reaches 4,000 RPM.
• The noise should disappear immediately if carbon deposits are the cause.
NOTE:
• If the customer reported a noise that exactly matches the symptoms listed above, but you cannot
duplicate it, the cause may still be carbon deposits. Go to step 2.
• If the noise does not stop after revving the engine, or you observe any other noise that doesn’t match
one described above, go back to ASIST for further diagnostic and repair information.
2. To prevent this incident from occurring again, add a bottle of Nissan In-Tank Fuel System Cleaner
P/N 999MP-FSC00P to a full tank of fuel (in the vehicle’s fuel tank) according to the instructions on the
label.
• This product is proven to reduce carbon deposits on pistons and combustion chambers, as well as
cleaning other components of the fuel system.

Hope helps.

Maybe it's not the water pump that is making the knocking noise.

Water pumps generally don't make knocking noises.

It could have a spun camshaft or main bearing if you hear a loud metal to metal knocking noise.

The coolant pressure cap hose that connnects to the radiator:
Is this an overflow hose that leads to an overflow tank? If so, the hose may have a restriction in it.

sound like an internal engine problem. either one or more of the pistons has "piston slap" and that knocking will diminish as the engine warms up or possibly a rod bearing is worn out. have a tech do a manual oil pressure test to make sure the oil pump and main bearings are ok. piston slap or knock that decreases when the engine warms up is not that serious, but a rod bearing knock or possible oil pump failure should be taken care of asap.

the chances are you have done the shell bearings on the cranck shat in or the big ends if it is a loud knocking noise or possibly the turbo (is their any smoke from engine bluey in colour if this is so engine has been damaged it could also be the camshaft too without hearing it it could be anything )hope i have helped you