How to fine defrost noise when turning heat on

no info generic answer check fuses relays control switch and fan motor

Inside the box where all your component inside the ac box r little doors that open to give you defrost n heat there like 4 small door you need to see if one of those door not is stuck inside a peace of napkin or paper that will make it do that noise get back good luck

Are you referring to the blower NOT blowing air or it is blowing air but will not direct the flow to defrost?

bad motor or transmission mount.

That is your a/c compressor kicking on and off to create air to the defrost. The a/c compressor will only kick on when the a/c is on or the defrost.

you have a vacumn leak at the front hub seals that is exhausting the vacumn supply which in turn the default for the heating system is defrost with a loss of vacumn.

a/c compressor may be seized. A/c compressor kicks on when in defrost, a/c, floor/defrost modes any time temperature is above 40 degrees F. That will burn the sepenine belt and stall the engine.
Try turing heat on floor mode only & see if ok.

your a/c is going to run on defrost that is normal. but the if the noise is coming from the comp then you have bearings or clutch going out on your compress. if you want to delete the comp buy a belt for your truck with out a/c and see if you can make it fit sometimes you can do this.

i beleive these are a vacuum system. if air temp is in cold position you will get no heat. listen for hissing noise with motor turned off but key on. if you hear hissing noise you have a hose broken or off. you will have to find it

You probably need to replace the thermostat.