My Core One started its life fine - very few 'head bangs'. Gradually got worse over time. 

My gantry is completely square. My belt tension has been set to the new recommended values. Yet I get excessive head banging. 

If I reset the printer due to excessive head banging that doesn't stop, it then seems to head bang only 2 times each side and continues fine. For me, this rules out a gantry issue, as if that was causing the problem the head would continue to bang even after a printer reset.

If I reduce tension on both belts back to the old values, head banging seems to reduce (hence thats what I've done), but I still find it excessive.

I still get some resonance noise, but it's not too much - certainly not enough to bother me (I work in the same room as the printer), so I'm not too concerned with that. 

My other printer (non-Prusa) has no 'head banging' at all, and seems to give me better quality than the Prusa at the moment, so that's the one I find myself opting for 8 times out of 1o nowadays.......

There's something wrong with your machine then I think mate, mine doesn't make any loud , or even not loud buzzing noises.
And with the head banging, how many individual bangs are you getting? You can select 'auto home' from the menu to save starting a print.

Im pretty sure optimum is 12 bangs, (4 followed by 2x4)..its not really excessive imo...any more than that and 99% of the time the gantry isn't square or the belt tensions are off. 

 I believe you are missing my point, mate. 12 Head-bangs is NOT optimum - nor is 4 or 2.  Head-bangin is a design defect that you have normalized in your head because Prusa said "Oh 12 head-bangs is GREAT!  My Voron 2.4 is also a core x-y machine with much more complex kinematics and it doesn't do head-bangs at all; it uses two $0.10 micro-switches and some printed parts.  Head-banging is a ridiculous way of saving a few cents off the cost of the printer, while putting extra wear-and-tear on the hardware and pissing off the very people you need to talk up the product.  Prusa himself ought to be on this forum apologizing for this and promising to make it right for all of us who unknowingly bought a lemon.

Posted by: @frank-8

My MK4 was my second Prusa printer, and I recently converted it to Prusa Core ONE. I have to agree with others that this was NOT an unalloyed pleasure, and the 'head-banging' is one of the two main buzz-killers (the other one being the loud buzzing noises when the toolhead motion resonates with the cheap sheet metal enclosure sides, back and top). I also had a heck of a time getting the belt tensions set to the point where the printer would actually get through the 'squareness' check. This involved multiple chat sessions with Prusa tech support, and honestly I have no idea what I did to actually get it to work. I'm not in any hurry to repeat that experience, so for me 'good enough' is good enough, and my prints are still coming out beautifully. The Core ONE is a wonderful improvement on the MK4 in terms of filament capability with the enclosure, looks a lot nicer than my MK4, and fits in the same space on my desk. However, Prusa made some design/fabrication choices that significantly detract from my (and others, from the number of posts on the subject) user experience. Had I known about the 'head banging' and loud buzzing noises during prints, I would have stayed with my MK4.

There's something wrong with your machine then I think mate, mine doesn't make any loud , or even not loud buzzing noises.
And with the head banging, how many individual bangs are you getting? You can select 'auto home' from the menu to save starting a print.

Im pretty sure optimum is 12 bangs, (4 followed by 2x4)..its not really excessive imo...any more than that and 99% of the time the gantry isn't square or the belt tensions are off. 

@gb160 (quote is not working for me) I am referring to this:

Posted by: @briange

I received my Core One kit a few days ago, assembly was not easy as MK4, but I enjoined.

After a couple of test I was very happy with print quality, but the head banging and after reading the comments in the forum, encourage me to try something else, so:

1) First I checked & tensioned the belts as Prusa App mention: Head to the front right and 98 & 92hz, ok with that but with no less than 50 bangings or even homing failure.

2) I found some articles with the method 85hz in each lateral belt with Head back to the center. Things go better but here the banging goes between 20 and 30.

3) Looking for more, like arachnoid webplace, mentioned that Prusa App is not good depending on mobile phone, so I download spectroid and use that to listen to belt frecuencies and... adjust tensión to 98hz &92hz with head front / right and thing go worst... in 5 homing tries, 3 failures and the other with no less than 50/60 bangings, bumping, hitting, ggggrrrrrrrr. 

4) I start playing dinamically with belt tensión till homing went Ok, 2 moves to the front 2 o 3 to the right, Then I checked belt tensión. head (means print head) to the center and back, lateral belts were at 89 hz. 

I'm making some print test including square patterns to check printing geometry, first small printings are good.

Maybe It can help someone. 

cu.

There's probably dozens of posts in the forum  about the proper way to tension the belts and what apps to use.
(I use the Gates Carbon Drive app as it works really well with my Pixel phone.)

1. Check your X/Y motor pulleys.
2. Loosen the belts
3. Square the gantry
4. Tighten the two screws equally side by side.
5. Pluck the belts across the gantry.
6. Alternate each side as you approach the right frequency. They'll interact (as Jurgen has said, the belts connect at the extruder, so tightening one screw tightens both belts.)
7. Check that the gantry is still square.

You will not be able to eliminate the banging, as that's how it measures homing. But it should bang just a few times before finishing. 
Monitoring the printer with a terminal interface might give you some insight into what it's seeing and perhaps why it's not homing properly.

After a couple of test I was very happy with print quality, but the head banging and after reading the comments in the forum, encourage me to try something else, so:

1) First I checked & tensioned the belts as Prusa App mention: Head to the front right and 98 & 92hz, ok with that but with no less than 50 bangings or even homing failure.

2) I found some articles with the method 85hz in each lateral belt with Head back to the center. Things go better but here the banging goes between 20 and 30.

3) Looking for more, like arachnoid webplace, mentioned that Prusa App is not good depending on mobile phone, so I download spectroid and use that to listen to belt frecuencies and... adjust tensión to 98hz &92hz with head front / right and thing go worst... in 5 homing tries, 3 failures and the other with no less than 50/60 bangings, bumping, hitting, ggggrrrrrrrr. 

4) I start playing dinamically with belt tensión till homing went Ok, 2 moves to the front 2 o 3 to the right, Then I checked belt tensión. head (means print head) to the center and back, lateral belts were at 89 hz. 

I'm making some print test including square patterns to check printing geometry, first small printings are good.

Maybe It can help someone. 

cu.