The pulleys on alternators actually have a one way bearing/clutch in them, so I'm thinking something may have gone wrong in there but who knows, it's the only other thing on the belt and the sound goes away when the belt is removed, also yeah I did check the belt, it looked fine. I should add that nothing visibly moves/shakes when it knocks, also it being loose wouldn't be affected by engine temperature (since it only knocks when warm)

Edited 30 August, 20214 yr by LightRobin

Most of the things like the tensioner and alternator will be more like the old 'fan belt' noises which aren't knocking noises.  I think it's a good idea to check for anything that can be reasonably done to reduce any strains or tensions with the use of the belt.  The belt can transfer some strain and tension from one area to another and conversely strains or tension areas can transfer to the belt to transmit - think of a recent global event, it's all about interactions.

 

Replacing any part that is faulty or severely underperforming will help but replacing parts that are performing tolerably or reasonably depends on budget and expectations of improvement and you don't want to replace parts that are working more than reasonably as you may want or need to use the funds elsewhere.

 

I'm sure you've researched this but a couple of general offerings.-

1. Alternator Clutch Pulley Symptoms: Diagnosed and resolved overrunning alternator pulley - By Dencan Brain (text) - https://toolsbible.com/alternator-clutch-pulley-symptoms/
2. Testing Alternator Pulley Clutch - https://www.youtube.com/watch?v=1Duj1jh1rlAa 

 

 

And a VW/Skoda specific, (must be a hybrid accent?) - Alternator clutch pulley diagnose and replacing, VW / AUDI /SEAT / SKODA https://www.youtube.com/watch?v=fyosuYbPxr4 

 

Cheers.

 

14 hours ago, LightRobin said:

it's the only other thing on the belt and the sound goes away when the belt is removed,

Sorry, I meant to put, it's the only thing driven but not the only thing on the belt there's the means of drive.  Removing the belt takes the load off the driving end reducing or removing strains and tensions as per Wino's earlier post.

 

Also sorry my mind defaults to older cars with older design's of ancillaries with alternator pullies being held on by large nuts, I am very old and feeble-minded.

 

 

Edited 31 August, 20214 yr by nta16
reference Wino's earlier post