Buzzing from front (windscreen or front door??) window: look for loose plastic trim that could be being shaken about in the breeze.
Knocking from back end: on level smooth road or going over rough? Anyway firstly, suspension up crawl underneath & look for loose exhaust banging against body/chassis.Have a shake of ex. pipe `n` see if it touches. Good idea to try to localise any noise by opening windows, and getting passenger to hang head out of each side to decide where noise coming from.
