These air pumps are noisey. Always have been. Always will.
They also very seldom break.
Save your money and let it run. It'll probably never go out. It only functions for about 45 seconds on cold start to reduce smog emissions.
Besides, they're over $1,000 from PartsShop, and even more from a dealer.
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".