I have a saab 9-5 2.0t 2002 when revving vehicle at about 2000-3000 rpm i have a rattle / knocking noise but not at any other time . Cannot locate where it is coming from no other problems can you help

if on a V 6 petrol @ 1500 rpm
could be the knock sensor
distributor timing might be out
or serp belt tensioner bearings

if a diesel i would expect a rattle@1500 rpm

If the Check Engine light is "flashing", you should take it to a shop as soon as you can. If it steady-on, then you may have some time. Depending on where the noise is originating from, it could be anyting from a damaged turbine or an unruly valve. Can you be more specific?

If this vehicle was driven without oil, the rattle or knock you hear is more than likely a damaged main bearing or rod bearing...sounds like its time for a QUALIFIED PROFESSIONAL to listen to your engine run and give you his opinion... Good Luck!!!

Bang on the catalytic converter being careful not to get burnt and see if it's loose causing a rattle. Until you determind what the problem is don't drive the vehicle. The other possibility is that you may need an engine. If what you're hearing us a connecting rid knock.

No it isnt a knock sensor the knock sensor job is to detect a knock noise and ****** timing. The knock that it is looking for is from octane or fuel or pinging that creates N0X s. A pollution gas. The knocking noise that you are hearing is different. If it is a multiple noise ar a rattling sound that will be the valves. There are other noises like a piston knock this knock is a sharp metallic noise, If the knock occurs only on acceleration that noise is a crankshaft noise. You need to check you oil level and make sure it is corrects. Look at the oil condition do you see silverish or whitish condition,is the oil deep black.

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.

As you might suspect, it is hard to detect a rattle source, unless one actually drives the vehicle. My best guess is that the KNOCK SENSOR is either working erratically, or not working at all. This type of failure more or less matches your description. Have the engine scanned, and if sensor is found damaged, it is easy and inexpensive to replace. Driving for extended periods of time (months) with this noise (knocking engine) , will cause permanent damage to engine.

I had the same problem on my 2006 Lucerne and it was the engine mount located on the front of the vehicle behind the radiator.

there are heat shields that can come loose after time. and at surtain rpm will make rattle noises. that is common with ford explorers

have they checked front c.v. joints, as far as knocking noise it could be several things.