When we moved in to our house about six months ago, we noticed very low pressure in the kitchen sink, with pulsing water. We've since replaced the faucet and hoses, with no improvement. Today we replaced the valves. We found some white stuff in the old hot water valve (photo below). The water pressure did improve a little after replacement, but not a lot. The pulsing is still there. It is very frequent on the hot water, and every couple of seconds or so on the cold. Does anyone have any ideas on what might be causing the low pressure and pulsing?

For further info: It's city water. This is the only faucet with low flow and pulsing. The lines to the faucet and connected tightly and not kinked or anything.