Engine knocking

When I start my 2002 Mustang V-6, the engine makes a knocking sound for about 15 to 20 seconds. I have taken the car to a couple of repair shops, but they are uncertain of the cause. Could this be normal for this car?

No, it is not normal. Could be a bad valve lifter and/or low oil pressure for a while after startup.

Thanks for your response. I just had the left exhaust manifold replaced, which was cracked. I also received new spark plugs and a wiring harness. The mechanic charged me $900 for these repairs and a new alternator. Although the knocking is better and now only occurs when the engine is cold. I’m thinking that I may have been taken.

If its a lighter tapping noise it could be in valve train but if its a heavier knock it is bottom of motor, maybe a rod bearing.
Top of motor noise is not real bad as long as it does not get worse but bottom of motor is bad and will cost $$$ to fix.

The car is 7 years young now. Even if the knock is still present it does not mean these other iitems were not needed, and I too would have recommended replacing a cracked exhaust manifold even if it were not knocking. I don’t see anything in this list that suggests anything suspicious for a vehicle this age.

Has the vehicle been treated kindly, not raced or neglected?
How many miles are on it?
Does the oil pressure light glow while it’s waiting to stop knocking?

My first inclination is to suggest a bad bearing, assuming that it’s actually a knocking sound and not a ticking. but more information could change my mind.

Recalling other episodes a bad exhaust manifold can allow cold air in to cause problems with the valves. A compression test can determine the soundness of the valves but I am thinking you are probably needing a valve job.

Try a new Motorcraft oil filter first.