'86 420SEL: Noisy Fuel Pumps

[Randy]

Hi, My car, an '86 420SEL with 151,000 miles, did not run when I bought it in '03, due to failed fuel pumps. I replaced the pumps with the correct Bosch pumps, changed the fuel filter, and got it going. Since December 2003 I have put about 5000 miles on it. Sometimes the whirring from the pumps is very noticable from inside the car at idle, such that last night my passengers asked if we "are going to make it". It has never offered a minute's trouble since I have owned it. Right now the fuel tank is about 2/3 full. Is there some other component in the fuel system which can cause this if it is failing, or is this the nature of the beast, or? Thanks.