engine sounds and upgrade advice

[Cream]

sometimes when i start the engine it doesnt start until after a couple of seconds and it makes this loud screeching noise. is that the spark plugs? also i want to put in bigger fuel injectors and a m30 afm. any advice on the brands of injectors? (motor has 255k miles) but still runs strong.

[eugeman]

check the tension on all you belts

[StereoInstaller1]

sometimes when i start the engine it doesnt start until after a couple of seconds and it makes this loud screeching noise.

Check for cats.