Steven,  There are a ton of folks on this site more experienced than I, but I have been doing this a while myself.

I myself would consider a few things before anything else.  On a longbow, string and limb vibration sound like just that.  An arrow striking the handle or rest area sounds different and more violent.  

Can you guess which it is ?

The bowyers website recommends 6.75" brace height for that bow.  I wouldn't normally go less.

For a normal 28" draw, and split finger release, I would place my nock point starting at about 1/2" above level and nock beneath it.  For a very long draw you may need to raise it up higher, even maybe getting closer to an inch, but I am just gonna guess that your bow / your draw doesn't require that high a nock point.

If the brace and the nock points are good, and I would check to be absolutely certain these are as you say, then we start getting into the arrow spine.  Trial and error will tell, unfortunately some bows need way heavier arrow spine (I believe Black Widows are notorious for this) and some are not near so picky.  I would take a wild guess and think the lighter spined arrows you mentioned should work best for that bow, maybe even a tad lighter yet, so heavier heads on those shafts might make them work.  You say that they are woodies.  Are they 11/32" diameter ?  That makes a difference as compared to some of the carbons.

Is your bow / rest material showing any sign of contact ?  Maybe place some fresh clean masking or paper tape on the rearward surfaces of the strike plate / rest area, then take one of your arrows and rub some stuff on it.. (shoe polish paste comes to mind), on the rear end of the arrow only, like, the last 6 inches, and see if it leaves a mark anywhere (for reference) after the shot.

If it does, where the mark is might help you guess better what is happening.

Lastly,  you say your other bows don't exhibit this.  What are their lengths ?  Is this little guy the shortest bow you have ?  Maybe the shorter bow is causing a smaller string angle, causing a bit of finger pinch, and a less clean release, that you don't get on the other bows.

So many things it can be, so you need to change one thing at a time and see what it does.

When you do, tell us what it was please.

ChuckC

Very thought out and concise response chuck. I'm with you.

Thanks to all so far for the help. Will keep you posted on what is happening.

Ok so I've put fur string silencers on the bow, moved the brace height to 6 3/4 and moved the nocking point to half a inch above square. It still makes a bang but not the BANG from before. So thank you. It has a hair strike pad on the bow which seems to be very hard, my other two GN have soft leather with some give to them. Do you think if I change the strike pad it would help? 65-75lb arrows still seem to be the best arrows to use with it.

What string material are you using. I had a bow that if you used anything but a low stretch string the bow would be loud.

Steven, do you know what your arrows weigh ?  Physical weight of the arrow with point ?

ChuckC

Based on my GN Critter Gitter, I believe your arrows are too stiff.  Try some heavy points, 160 or 190 grains, on your 50-55's and I'll bet you will stop the arrow slap.

Hi,
The string is what was sent with the bow from GN so BCY Dynaflight 97 ?
The wooden arrows are 535grn some a little more some a little less, none under 500grn.
When I shoot lower poundage arrows the banging gets louder.
Thanks for your time

Steven, I guess the next logical chore is to dig up a few even heavier shafts, or,  try some carbons, just to see what happens.  They are a bit stiffer and they are normally skinnier, which changes things.  All these things give you answers and may help you understand that bow a bit better.

Keep going.  Its a good bow.

ChuckC

Have you considered calling Jerry and talking to him directly. He's a great guy and I'm sure will take the time to answer all your questions and offer advice.

Softer string material on a Great Northern always helps..There are better alternatives now to some of the "FF type" strings..softer, such as 450 plus, Dyneema, or skinny strings from some of our sponsors here..best of luck.

Hi,
I will try some carbon arrows and see what happens.
Any idea of the email address for Jerry or GN as I cannot seem to find it on the website?  
Thanks again for all your help.

Can anyone give a name or two of sponsors who may be able to do me a new string. I think my GN fireball has a skinny string but no idea what it is and my GN critter gitter sp has a D 95, maybe??

I suspect the bow is fine. Sounds like your arrows are smacking into the bow.

Like others, I suspect your arrrows are too stiff.  For comparison, I shoot about 55 pounds and I use 29" ICS 500 carbon shafts with 100 grain inserts.  My arrows fly like they've been shot down a pipe.

Nocks too tight?  Dacron string?   Also try turning your nocks for better clearance.

Could also be your release.  Try getting a good deep hook on the string.  Don't hold the string out on your fingertips, but deep in the first joint.  Seems counterintuitive, but you'll get a better release.

Thank you all for the advice.

Ok so I have made sure the nocks are loose, have tried arrows which are 500gr plus in weight and are from 40lb to 75lb. Carbon and allys are no good as they are loud coming out the bow. 45lb to 60lb are ok but it still seems to like the 65lb to 75lb most. It makes a bang but not as loud as all the other arrows.

I am putting a wooden frame together to try and paper tune and will let you know how that turns out also. Thanks again for your time and help.

What are you actually drawing though?I didn't see
except arrow length.I ask because if I short draw(and not on purpose)certain arrows really clang against riser.Drawing fully cures it.
A really short draw will sound quiet also but you'll know from arrow drop.
Hart2hart

Well, I changed the brace height to what it says on the website,  then put wool string silencers on, using 62lb arrows which are 500 gr. The bow is now whisper quite.

Cool