When i turn a/c or heater on, there's a noise that comes on and goes away after few seconds or minutes.

 

it's the A/C compressor, when it is engaged (which cycles, reason for the varying times)(and you say heater, on defrost then?)

but yeah mine does the same thing, does not really bother me though, cause my windows are up most of the time, which mutes it out

 

so, this is normal right?

 

basically every car does it, some are worse then others though (and newer cars do it alot less though)(our cars do seem to do it a bit more then others though , but basically unless you want to replace the compressor, not much you can really do about it (btw: easily $1000+) (you can also try adjusting the shim on the clutch pack, but never had a whole lot of success with that though; or replacing the clutch, but again not much success (the snout on the compressor was actually worn, causing the clutch to wobble, and go out in a short amount of time)

and as said the windows cover it up pretty well, along with the radio on, and you just get use to it really