I had a tinkling noise coming from the engine when under load. The main agent diagnosed the alternator belt tensioner and replaced it, along with the belt, for £230, which cured it. Now, just over 6 months later the tinkling has started again. I notice the small print on the invoice says 'the company warrants its work for 3 months or 3000 miles'. I've only covered 1500 miles but clearly over more than 3 months. Are their terms reasonable?