LOUD KNOCK NOISE WHEN SHIFT TO FIRST AND SECOND GEAR

Knock sensor controls ignition timing. It should have no control on transmission shifting. Did you disconnect/remove anything else to access the knock sensor? Was the battery disconnected? If so, a relearn procedure may be required for trans module etc relearn shift points while you drive the vehicle

you fail to menyion what kind of car and which engine. I can only guess that this is what is known as spark knock which can be caused by several things, most common would be low octane fuel. another more critical cause could be improper timing.

5.000rpm's high revs and you run into problems with valve bounce ( hitting pistons) ,ring slap, gudgeon pin knock, big end noise and possible main bearing noise . You may also be getting a hydraulic lock in the hydraulic followers that is holding the valves open too long. Unless the engine has been specifically built for these rpm's any loose ,worn on unsuitable part will cause problems I am thinking that you have around 100.000 miles on the clock after 7 years and the motor is not young Ford V8 engines specifically built for a 500 klm race are limited to 5.500 rpms because they destroy the timing chain if driven over that speed .

If this is covered with a warren tee I would take it back where I bought it. Sounds like a faulty bearing or something is sprung and hitting when it starts up.

It sounds like you have what is called pre ignition knock. Have a technician drive the car and see what they think.

The shift drum would not make any noise, ever. The drum will outlast all of us. All it does is move clockwise and counterclockwise as the rider pushes the shift lever up or down as needed. Go to an empty parking lot or roadway and start out slowly in 1st gear, slowly gaining speed. Does the knock show up? Now go into 2nd gear and slowly gain speed. Is the knock there? Do the same for all the gears. If the knock is only in one or two gears the problem is a broken gear tooth. When the broken gear is replaced, also replace any other gear the broken gear meshes with. Whatever broke the tooth also put the same pressure on the meshing tooth. If the meshing gears are not replaced you will have the pleasure, ( and expense ), of doing the repair all over again when the cracked tooth on a meshing gear decides to break off. This usually happens within the first hour of riding the "fixed" bike. If the test shows no knock in the gears, then chances are the knock is a cam chain needing to be tightened. Please rate my answer. Thanks.

You will need to rebuild yours

Never install some elses used unit

If the shifting makes the bike "slam" into gear then the engine is running too fast. Put the bike in first gear when the engine is running at a slow speed. When shifting into second gear, let off the throttle as you shift. Do not power shift, use the clutch always.
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The rattling noise could be many things. Is something loose on the bike? Are you using premium gas? Lower grades of gas can cause pre-ignition / detonation / engine knock < what ever you care to call it. This is VERY bad for a motor. Only use premium gas and do not us gas with Ethanol.

Top rating for this answer? Thanks!

That is what happens when you try to shift gear with out depressing the clutch pedal while changing gears.

as odd as this may sound, try replacing the fuel filter.