Knocking sound

Just curious as to why a top mount would make a ‘twang kung boing’ (love this description, absolutely bang on!) noise as it’s just (as I understand it) a bearing helping the strut to rotate. I’d have thought a worn top mount would rattle as it hits an uneven surface, much like mine does. But then, when does logic come into it, and what do I know?!
 
Just curious as to why a top mount would make a ‘twang kung boing’ (love this description, absolutely bang on!) noise ...
As far as I know it goes twang kung boing when the bearing in the top mount no longer rotates making the spring scrape across the bottom of the top mount bearing, skipping as it goes hence the spring like noise. Eventually if the bearing is not replaced this could cause the spring to break at the top - I have had this happen before and the car was ever so slightly off balance as only few centimetres of the spring broke off (I found it on the drive) and tended to turn to the left as it was slightly lower on the left side.
 
Well, I took Tarkus out to the nearest retail park after 5pm to test going round in circles with full lock on. It did feel a bit weird as I could hear in my mind the few shoppers left looking over to the the far end of the car park and thinking "what's that strange old guy with the silly little car trying to do donuts for..." ?
Anyway I could not get it to do any knocking noises, so maybe it was the liner after all? Though I am still not convinced.
It has to go in for a service anyway so I will ask the garage to check the CV joints.
 
Well, damn, the noise came back after 10miles or so on my commute this morning. Is it unusual for a CV joint to be this intermittent if it's about to go? It was definitely more prevalent on engine load - accelerating and going up hill and not just cornering either. Short journeys, tight cornering and going round in circles did not seem to bring it on over the weekend.

I was wondering if it's just bearings that don't start knocking until they have heated up a bit or something? When bearings start failing, from my experience it is more of a whirring noise that knocking though.

Anyway, I booked into a garage near work for tomorrow , so I guess I will find out then. I don't know if I will leave it at work until tomorrow or risk driving it home...
 
I had a similar gremlin last week made a whuup whuup when turning right, the more speed /energy = more noise, I expected a CV joint or wheel bearing, it turned out to be just a loose driveshaft cover, like this:
 
Another obvious one is the bonnet - which I think you mentioned already. Make sure you cant move the corners down and if you can then pack out the area with plastic from a bag or bubble wrap. When you go over bumps the car flexes and if the bonnet isn't snug in the corners they can "tap" on the chassis making a knocking noise.
 
I have got a new CV joint now. After driving figure of eights around the car park last Monday evening and not getting any knocking noise, but then getting such bad knocking after 5 miles into my journey home that I had to call the AA out. The AA man showed me the split in the CV boot which I had not seen myself as I had not turned the wheel back and forth to show how it gaped like he did. The AA man greased the CV joint up and recommended not to go any further than the garage. So I got to the garage the next day but they were too busy to do the CV joint, boots and several other things that they "found" to do so I was without the car for a week.

I guess lesson learned - even if something does not happen on short journeys does not mean to say that it is good to drive on longer journeys. It must have been that the CV joint only started knocking after heating up sufficiently for the bearings start to cause the knocking.
 
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