What could be causing this?

Some of the debris from the water heater likely made its way into the
supply for your problem faucet.

Try these steps. Stop when you have success.
1) Clean the faucet aerator.
2) Clean muck out of all the tiny openings inside the faucet.
3) Clean muck out of the supply line under the sink.
4) Flush the undersink cutoff valve into a bucket at full force.
5) Rig a hose to run cold water backward through the faucet into the water
heater. You may be able to do this with your back yard bibcock, but most
likely you'll have to use the neighbor's water.
6) Call a pro.

Let us know how things go.

Ok, I'll give it a shot and let you know how it goes.

Thanks for your help.

-Randy