I had the same grinding noise for about 2 months, gradually getting worse, asked my local garage who service the car to take a look when MOT was done, was told it was fine, so had the lexus dealer take a look (cambridge) and they confirmed it was the water pump. They offered to change for £320. The water inlet also needed changing but they didn't charge any extra (although it meant they had the car another day while waiting for parts). Happy its sorted. Owned the car for 9 years and its had one water pump, two batteries, an alternator, set of spark plugs, brakes every so often (callipers, pads, discs etc). never broken down other then the alternator, but that was a case of not starting at home. Fantastic ownership experience so far. Also had the wheels refurbed but other then that its as i bought it.