K80

Hi I have recently been talking with my local BMW dealership in North Wales (no names needed), they recently told me i had a slight noise coming form the engine and they thought it could be the timing chain, but suggesed i put it on diagnostic first, I did, came back with needing the belt, tensioner, pulley, and dampers changing £650+. when they checked it by taking old belt off noise went away, went ahead with the repair. Picked car up, they said the noise is still there and would be the timing chain, they contacted BMW to see if they would offer goodwill, they did 100% of parts and 50% labour, Dealership want me to now pay other half = £750 plus VAT, they wont budge, the chain is not been caused by my driving but from the recent report which i am sure you all know about. I cant hear too much of a noise, the car is a diesel and has done 108,000 or thereabouts, should i be worrying that chain will get worse quickly, should i persue garage if is. secondly, tyres, run flat or non runflat, i do a lot miles and am having to change the tyres regularly. i note from the forums here that the car is set up for run flats in that it warns when tyre pressure is low or when suspension is being adjusted for road (the little A in a circle), i am right? can i buy non runflats and still be safe? many thanks K