First Question: Why does excessive PSI in water line reduce kitchen faucet water flow?

Short Version:

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Four year old Delta faucet worked great until apparent water pressure changes were made to the home, now it's down to a trickle. However, no other faucets had any noticeable (negative) changes.

The water comes out of the faucet at good flow for about 1 second, then reduces quickly and starts a (relatively mild) knocking sound on the pipes. Flows stays at a trickle. No knocking after the faucet is shut off. Nothing else in home triggers any knocking. The knocking *appears* to be in the home piping, as it's much louder in the bedroom than what can be heard at the faucet itself. Though this may be illusory due to sound acoustics via piping and walls.

If I *reduce water flow* into the faucet, by half-way closing the valves from H&C below the sink, it *increases* from 25% to about 75% water volume.

Background:

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Let me first state I've read through dozens of posts and done all the troubleshooting methods for DIYers. I typically do before posting.

Events Triggering Change:

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During the city installation of new water meters (and changed lines in the street), the kitchen faucet started acting funny -- air in the lines, sand in the aerators, reduced pressure, then normal. Figured this was all normal.

After they finished: I cleaned out all the aerators (three times over the next month) and also ran all the faucets in the house to eliminate all air and discolored water in the lines.

Troubleshooting Steps Performed:

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* Aerators cleaned, replaced.

* Removed and cleaned the hand-held sprayer.

* Ran a small brushed-snake down hand-held sprayer line to confirm no obstructions.

* Removed the faucet handle and verified no obstruction and the 3 holes (2 supply, 1 out) were clear.

* Ensured copper piping into faucet (below sink) weren't bent, pinched, etc.

* Replaced old valves from the wall source with new 1/4 turn.

* Cleaned out inside of supply pipe stubs with small brushes (found small amount tiny bits of rust/metal/calcium substances).

* Confirmed water source pressure strong by disconnecting supply to the faucet (the copper intake pipes) and spraying water into a bucket directly from the H&C metal-braid flex lines. Water pressure and volume is strong.

I suspect I had a 1 1/4" piping into the home and city reduced it via new 3/4" meter placed on the home. Speculation though...

Second Question: How can I fix this problem?

My dirty faucet and sink pic below....