About a year ago I  put together an  AR-15 20"  HBAR  using  Bushmaster upper, lower, bolt carrier and bolt and std A2  buttstock and  buffer assembly.  I used a Fulton Armory barrel.  It work  great, it looks great  it shoots nice  but  when firing  it    the noise of the buffer spring  sound like  an old daisy air rifle.  I  have never experienced this  noise  in my  Colt Sporter carbine so I am wondering  if there is  something wrong with the  Bushie parts.  It really does not  seem to affect the functionality of the weapon  but  the  sound is  pretty annoying.    Any suggestions ?

Thats the sound they are supposed to make. you can get rid of some of it by putting a good amount of oil into the buffer tube, but i wouldnt advise it.

I think the sproing noise is accentuated by the standard A2 stock, when I slipped a VLTOR A2 over the extension, the noise was almost gone. When I changed to a VLTOR telestock and extension, it hardly makes any noise. YMMV.

That noise is normal.  Sproing-ng-ng-ng!  Don't worry about it.

if it really bothers you, to the point of distraction, just a dab or 2 (not a pound) of grease, lightly rubbed on the spring will quiet it down,,,
but it will get REAL dirty!