I had a new bathroom faucet installed yesterday by a professional plumber. I did not notice it at first, but the unit WHISTLES when the faucet is turned on. Also, the water pressure does not seem as good as my older faucet.
He turned off the water from the SHUT OFF VALVES under the sink to do this job.
The faucet is washerless.
Please advise anything you can on this. He will come back, hopefully at no cost.
Thanks

Other than making sure the shut offs are all the way open it's likely the new faucet has a different aerator that supposedly saves you water usage by restricting the outlet pressure. If you still have your old aerator you can exchange them. Should fit. Please let us know how you made out. Hope it's as simple as I made it sound.

Not sure about the whistle but, low flow is common in newer faucets. Supposedly saves water.

Consider yourself fortunate, most faucets never learn how to whistle...but seriously I am with Talaniman about the shut-off valve not being fully opened. Turn the knobs all the way to the left. As mao641 mentioned, newer plumbing fixtures have a flow restrictor built into the aerator. If the whistle persists, then unscrew the aerator and see if it goes away then. If you still have a whistle then have the plumber come back and swap the faucet.