Mech. fuel pump failure modes?

Well, here's the latest discovery..

As mentioned, the new electric feed-pumps made a terrible noise to the point where it sounded like the car was borken or something...

With the negine idling, the old mechanical pump disconnected but running, it made a very pronounced "wuhu-wuhu-wuhu" sort of sound. I put my thumb against the outlet, the sound disappeared and there was pressure against my thumb.. did the same on the inlet to find the sound disappearing again and positive suction building up. Hmmm

Before I changed to the electric pumps, that sound was there allthough not as pronounced as with the pump completely disconnected...

Could that have been an indication that the mechanical pump was in deed drawing air through that degraded hose between the tank and the fuel-line?

Disconnected the electric feed-pumps, put in a fresh piece of hose and re-connected the mecanical pump.

Started the engine, fuelpressure rose quickly, and there was no "Wuhu-wuhu" noise from the pump.

Did a relatively short test runn and got back home allright, still no noise from the pump.

I think I got to the root cause of the problem, and those dreadfuuly noisy electric feed-pumps are going out again!