Why is it always so quiet at Stamford Bridge?

Chelsea could be winning 7-0 and you'd still be able to hear a pin drop. And don't come up with the bull crap that Old Trafford's the same because that isn't true. It may not be as loud as it should with 75,000 seats but it's still pretty loud and especially from the Stretford end unlike Stamford Bridge where you can only hear the away support from the 1st minute to the final minute of added time.