poor driveability,hesitation,a buzzing noise on 2006 Ford Explorer

when the transmission shifts I hear a buzzing noise and the engine hesitates usually under a load but also on flat smooth roads.buzzing noise sounds under the hood andstops when load equlizes.I have changed the PCV valve and spark plugs but no improvement. Thank You for Your thoughts.

1 answer
Is the check engine light on? It would really help to diagnose this type of problem if you check for trouble codes. Have you tried this?