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Q: do i need a tune up? on 2005 Cadillac SRX

my srx cadi 05, is making a noise,next to the pully area, I remove the belts off and ran the engine and the noiseis there. what can it be? also when on highway and i go to change lanes or accelerate, the chk eng light comes on.i scanned and codes are 300, 304 and 306 came up.
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It means the #4 and #6 cylinders are misfiring. It could be spark plugs, ignition coils, incorrect air-fuel ratio, control module or wiring problem, internal mechanical failure, restricted exhaust.
The #4 and 6 cylinders are the middle and the last ones at the driver side.
It's not a good idea to run the engine in this condition, misfire can permanently damage your catalytic converters.
I think - since the noise is coming from the front, belt area - the problem could be with the harmonic balancer / vibration dampener. It's the pulley mounted to the crank shaft. This also could cause a misfire. The outer ring of the pulley could separate from the rubber and could slip on it, causing the noise. In same case it could also move backward and grind on the cam cover.
Check that area well and let us know what did you find.

The P0300 is for multiple cylinders misfire, the P0304 and P0306 is for cylinder misfire on cylinders #4 and #6. The noise may be the actual sound of the misfire. If plugs are old enough then start by replacing them. Other tune related components may be in need also. Your owners manual tells you when to do this. It is always better to replace these components before you have problems and not wait till have the probs. If recently changed plugs then will need to inspect #4 and #6 plugs for probs. Could also be coils or wires or etc.
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